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L-[3H]lysine uptake was measured in brush-border membrane vesicles prepared from intestinal mucosa of the European eel Anguilla anguilla. Lysine uptake occurred via 1) a nonsaturable component with an apparent diffusional permeability (P) of 0.58 microliter.mg protein-1.min-1,2) a Na-dependent transport system [half-saturation constant (Kapp) 0.16 mM, maximal transport rate (Jmax) 3.57 nmol.mg protein-1.min-1]; 3) a Na-independent transport system (Kapp 0.17 mM, Jmax 2.77 nmol.mg protein-1.min-1). Both carrier-mediated processes were accelerated by the presence of an intravesicular negative membrane potential. Hill analysis of L-lysine influx, over a wide range of external Na concentrations, resulted in a Hill coefficient (n) of approximately 2, suggesting that two or more Na ions may be associated with amino acid transport. The inhibition of lysine uptake by other amino acids was studied. Na-dependent lysine uptake was competitively inhibited by proline [inhibitory constant (Ki) approximately 2 mM] and may occur by a system specific for cationic amino acids. Na-independent lysine uptake was competitively inhibited by alanine (Ki approximately 1 mM) and may occur by a classic L system.

In a previous study, a Na(+)-independent, cation-preferring amino acid transport system was detected in preimplantation mouse blastocysts. The system resisted Na(+)-dependent inhibition by homoserine and so resembled the lysosomal system c more than it resembled the plasmalemmal system y+. We now report the presence of a cation-preferring system in unfertilized and fertilized eggs and cleavage-state conceptuses which also resists Na(+)-dependent inhibition by homoserine. The systems in 1-cell conceptuses and blastocysts are, however, insensitive to changes in pH in the interval of 6.0 to 8.0 and, thus, different from the pH-sensitive system c. Moreover, the relative strengths of the interactions of a variety of basic amino acids with the systems in conceptuses do not correspond well with the relative strengths of their interactions with either system c or system y+. Similarly, the system in 1-cell conceptuses can be distinguished from the system in blastocysts because L-arginine interacts about equally well with each of these systems, whereas the system in 1-cell conceptuses is inhibited more strongly than the system in blastocysts by most other basic amino acids. In addition, inhibition of the system in 1-cell conceptuses by some basic amino acids is Na(+)-stimulated, whereas Na+ does not affect inhibition of the system in blastocysts. Finally, L-tryptophan inhibits the system in blastocysts better than L-histidine or D-arginine do, but the reverse is true for the system in 1-cell conceptuses. Therefore, the relative activities of at least two forms of a novel, cation preferring amino acid transport process change during development of blastocysts from fertilized eggs. For convenience, the forms of the cation-preferring transport processes that seem to predominate at the 1-cell and blastocysts stages are provisionally designated systems b+1 and b+2, respectively, although these two systems need not represent entirely different gene products.

Lysine acetyl salicylate [1.8 g t.d.s. (Aspergesic 1,000 sachet)] has been compared to 400-mg ibuprofen tablets t.d.s. in a randomized double-blind trial in patients with rheumatoid arthritis using double-dummy technique. Both drugs proved effective in relieving symptoms. Three patients experienced drug-related side-effects with Aspergesic, and one patient with ibuprofen, that necessitated early discontinuation of treatment. Aspergesic was associated with a greater number of haemoglobin values falling below the normal range than ibuprofen. At the end of the study, eight out of 10 patients who expressed a preference selected Aspergesic for improving mobility whilst 15/24 selected Aspergesic for improving pain.

The lysine salt of d,l-2-(4-isobutylphenyl)-propionic acid (ibuprofen lysine) was administered as a single oral dose of 500 mg by means of commercially available coated tablets (Imbun).* To assess the absolute bioavailability of ibuprofen after its oral application as a lysine salt, intravenous injections of ibuprofen solutions containing 200 mg and 400 mg of the drug served as reference application. In a partially randomized cross-over design, 8 healthy male volunteers received three different single dose administrations which were separated by wash-out periods of 4 days each. Ibuprofen plasma concentrations were determined by HPLC using direct injection, pre-column enrichment and column switching techniques. From the results of intravenous injections one can deduce linear ibuprofen pharmacokinetics within the considered dosage range, with corresponding AUC0-infinity values of 3786 micrograms * min ml-1 and 7260 micrograms * min ml-1 for the 200 mg and 400 mg doses, respectively. The values of plasma clearances as well as those of different volumes of distribution showed remarkable constancy after evaluation from both intravenous injections. The absorption of orally administered ibuprofen lysine proved to be rapid, resulting in a mean peak plasma level (Cmax) of 31 micrograms ml-1 ibuprofen and in a mean time to peak (tmax) of 45 min. The absolute bioavailability of ibuprofen amounts to 102.7 per cent, indicating a complete absorption of ibuprofen when administered as its lysine salt. Drug tolerability was excellent for the oral administration of ibuprofen lysine as well as for the intravenous treatments with ibuprofen free acid. Only mild and transient adverse drug reactions such as mild burning or dragging sensation during injection or mild redness at the site of injection were reported.

Uptake of leucine, lysine, and arginine was predominantly Na(+)-independent in mouse conceptuses through the 8-cell stage of development, and two components of saturable transport were detected for each of these amino acids. Uptake of cationic substrates from solutions near 1 microM was inhibited most strongly by bulky cationic and zwitterionic amino acids whose carbon skeletons do not branch at the alpha or beta positions. By this criterion, system b0,+ accounted for most of the Na(+)-independent arginine and lysine transport in eggs and conceptuses throughout preimplantation development. A small, leucine-resistant, cation-preferring component of amino acid transport was also detected in these cells. Leucine uptake was inhibited most strongly by bicyclic, branched-chain or benzenoid, zwitterionic amino acids in eggs and conceptuses prior to formation of blastocysts. Therefore, it appeared to be taken up mainly by system L, while system b0,+ accounted for a smaller portion of leucine uptake during this developmental period. In blastocysts, in contrast, system L was less conspicuous, and system b0,+ was primarily responsible for Na(+)-independent leucine uptake. The Vmax values for transport of amino acids by system b0,+ increased by up to 30-fold in conceptuses between the 1-cell and blastocyst stages. In contrast, the Vmax value for leucine transport via system L decreased while the Km value increased between these two developmental stages. Although several explanations for these changes are possible, we favor the hypothesis that the density of system L transport sites in plasma membranes decreases while the number of system b0,+ sites increases during development of blastocysts from 1-cell conceptuses.

Several rat bioassays were conducted to evaluate protein quality and lysine (LYS) bioavailability (BIO) of Osmolite HN, a commercial enteral product, as affected by the severity of heat processing during sterilization and by storage of the products for 1 year. Without amino acid supplementation, the protein quality of Osmolite HN, as determined by protein efficiency ratio (PER), was lower than that of casein, regardless of heat treatment. With addition of the limiting amino acid, cystine, the PER of Osmolite HN was equivalent to that of cystine-fortified casein. Storage of the product for 1 year had no effect (p greater than 0.05) on PER, even though the products had darkened in color. Slope-ratio regression analysis (weight gain regressed on supplemental LYS intake) yielded a LYS BIO estimate of 94.4% for the Osmolite HN control relative to crystalline LYS. Partitioning weight gain into that resulting from LYS consumed in the basal diet and that resulting from the LYS supplement per se provided more accurate estimates of LYS BIO. This method estimated LYS BIO at 100% for the Osmolite HN products, regardless of heat treatment. With storage, LYS BIO decreased 11-12% in all of the Osmolite HN products. The decreased LYS BIO is of minimal nutritional significance in that overall protein quality of the products was not affected by storage. This is likely due to the fact that there is a plethora of lysine in Osmolite HN such that LYS is not a protein-quality limiting factor.

Systems of L-lysine transport in Schizosaccharomyces pombe are not constitutive, as at no phase of growth in a rich medium is lysine taken up. Transport activity appears only after preincubation of harvested cells with glucose or another suitable source of energy. If cycloheximide is added during this preincubation no transport systems are synthesized. After removal of glucose, the activity of the transport system decays with a half-time of 13 min. The transport of L-lysine into S. pombe cells from the stationary phase of growth preincubated for 60 min with 1% D-glucose is mediated by at least two systems, the high-affinity one with a Kt of 26 mumol/l and Jmax of 4.95 nmol/min per mg dry wt., the low-affinity one with a KT of 1.1 mmol/l and Jmax of 11.8 nmol/min per mg dry wt. The transport of lysine mediated by these two systems proceeds uphill. The high-affinity system has a pH optimum at 4.0-4.2, the accumulation ratio is highest at a cell density 2-5 mg dry wt. per ml and decreases with increasing lysine concentrations. Lysine accumulated by this system does not exit from cells. The only potent competitive inhibitors are L-arginine, L-histidine and D-lysine. The other amino acids tested do not behave as competitive inhibitors. Of the various metabolic inhibitors tested, the most potent were proton conductors and antimycin A.

True digestibility of lysine (LYS) in crystalline L-LYS.HCl and casein determined in cecectomized adult roosters was not significantly different from 100%. Subsequent 9-d growth assays were conducted to determine the bioavailability of LYS in casein, in L-LYS.HCl, and in a mixture of crystalline amino acids simulating casein's amino acid profile. Based on slope-ratio methodology, LYS bioavailability relative to casein was estimated to be 101.4 and 99.9% in L-LYS.HCl and in the casein-simulated amino acid mixture, respectively. Procedures also were developed for assessment of LYS bioavailability in crystalline L-LYS.HCl by comparing growth responses to intraperitoneally injected (IP-LYS) and crop-intubated LYS (CI-LYS) in chicks fed LYS-deficient corn-sesame meal diets. Graded increments of pH-adjusted L-LYS.HCl were administered twice daily in .5-ml doses during the course of 8-d growth assays. Chicks receiving CI-LYS also received .5 ml of IP saline at each dosing, and those receiving IP-LYS also received CI saline at each dosing. Slope-ratio multiple linear regression of gain (g) regressed on LYS administered (mg) was assessed for both ad libitum-fed and meal-fed chicks. Linear growth responses to LYS were obtained with both routes of administration and in both feeding regimens. The CI-LYS slopes ranged from 103 to 125% of those obtained with IP-LYS administration. These results support the view that crystalline L-LYS.HCl is 100% digestible and bioavailable.

Studies were undertaken to determine if dietary disproportions of amino acids would alter flux into brain of the amino acid present in the diet in a growth-limiting concentration. Rats were adapted to a lysine-limiting diet before receiving a meal of this control diet, alone or with added lysine or homoarginine (a competitor for lysine transport) or both, before intravenous infusion of [14C]lysine. The brain-to-plasma radioactivity ratio was lower in rats fed extra lysine or homoarginine than in rats fed the control diet, whereas lysine flux and brain lysine concentration were high in rats fed extra lysine alone. Flux and concentration were lower in rats fed homoarginine + lysine than in rats fed extra lysine alone. Other rats were fed a valine-limiting diet containing added valine, norleucine (a competitor for valine transport) or both, before [14C]valine was infused. Valine flux and brain valine concentrations were higher in rats fed extra valine than in control rats, whereas flux was lower in the group fed norleucine alone. Valine flux was higher in rats fed norleucine + valine than in the rats fed norleucine alone. Our studies show that dietary disproportions of amino acids can alter the flux of specific amino acids across the blood-brain barrier.

1. The availability of lysine in four meat meals (MMs), four meat and bone meals (MBMs) and two blood meals was determined using the slope-ratio assay with growing pigs, rats and chicks and with two chemical techniques. 2. The availability of lysine (proportion of total) in the eight MMs or MBMs ranged from 0.48 to 0.88 for pigs, from 0.49 to 0.88 for rats and from 0.68 to 0.88 for chicks. There was no apparent relation between the availability estimates for pigs, rats and chicks for the individual meals. 3. For the two blood meals, availability estimates were 1.03 and 1.13 for pigs, 0.81 and 0.80 for rats and 1.07 and 1.02 for chicks. 4. Values for the indirect and direct 1-fluoro-2,4-dinitrobenzene-'available'-lysine assays ranged from 0.77 to 0.88 and 0.78 to 0.93 respectively for the eight MMs and MBMs. There appeared to be no relation between these values and the pig estimates.

A gap1 can1 mutant of Saccharomyces cerevisiae with a single lysine transport system remaining was used to study detailed kinetics of this transport. Its half-saturation constant was 78 mumol per litre, its maximum rate of transport was 0.29 mumol L-lysine per g dry matter per minute, both parameters being lower by more than an order of magnitude in comparison with the GAP system. The pH optimum lay at very acid values of about 3, the temperature dependence without any transition point showed an activation energy of 48 kJ/mol. The transport was inhibited by common metabolic inhibitors (3'-chlorophenylhydrazonomalononitrile, antimycin, 2-deoxy-D-glucose, sodium arsenate) as well as by a membrane-active one (uranyl nitrate). The specificity of the system was extremely high, none of the natural amino acids acting as competitor to L-lysine. The maximum accumulation ratio attained (at about 5 mg dry matter per mL) was 100: 1-120: 1, in agreement with the measured protonmotive force under the assumption of 1 H+ ion being transported with 1 lysine molecule. The ratio decreased with increasing external concentration of lysine to as little as 4: 1 at 1 mmol lysine per litre. It also decreased with increasing suspension density and it was at extremely low suspension densities (0.2 mg dry matter per mL) that ratios of as much as 500: 1 were reached. Application of group-specific inhibitors showed that the active site of the carrier contains an essential histidine residue.

The objective of this study was to investigate the elastin repair process in the rat aortic smooth muscle cell culture after proteolytic injury. Although little studied in vivo, elastin repair is thought to occur through a sequential process involving enzymatic removal (debridement) of damaged fibers followed by synthesis of tropoelastin, its subsequent processing, and eventual incorporation into new insoluble elastin. A second repair mechanism of proteolytically damaged elastin in a culture system is reported here. Repair in this system relates directly to restoration of resistance to elastin solubilization by hot alkali. As expected, severe injuries were observed with porcine pancreatic elastase (PPE). Using PPE, only 6% of the elastin, relative to control, was resistant to hot alkali immediately after elastase treatment. 4 wk later, resistance to hot alkali had increased dramatically to a mean of 90%. Repair took longer after injury with 75 micrograms of PPE as compared with 50 micrograms of PPE. The limited elastic fiber proteolysis induced by either human neutrophil elastase or porcine trypsin was repaired in culture within 2 wk. Elastin that had been radiolabeled with [3H]lysine 4-5 wk before injury was converted from a hot NaOH-susceptible to a NaOH-resistant elastin fraction during recovery from PPE injury. At the same time, the frayed elastic fibers that were seen with the electron microscope immediately after PPE treatment were replaced by continuous bands of elastin that resembled those in control cultures. Restoration of NaOH resistance did not require a net increase in total cell layer elastin, suggesting that relatively little new tropoelastin incorporation into the cell layer was required for this type of repair. These results suggested a salvage repair mechanism for proteolytically damaged elastin.

1. Two experiments were conducted to assess the nutritional value of lupin (Lupinus albus)-seed meal for growing pigs. In the first, the availability of lysine was assessed using slope-ratio analysis. In the second, the effects of autoclaving lupin seeds and formulating the diets on the basis of estimated digestible or net energy were assessed. 2. In the first experiment, the availability of lysine in three samples of lupin-seed meal was compared with that in meat-and-bone meal and soya-bean meal. Availability of lysine in the five protein concentrates, using food conversion efficiency on a carcass basis as the criterion of response, was (proportion of total): lupin-seed meal no. 1 0.44, no. 2 0.57, no. 3 0.53, meat-and-bone meal 0.42, soya-bean meal 0.80. 3. Availability estimates, based on protein deposited:food intake, were: lupin-seed meal no. 1 0.82, no. 2 0.73, no. 3 0.70, meat-and-bone meal 0.27, soya-bean meal 0.77. These estimates had higher standard deviations than those based on carcass response. 4. Regressing the measures of response v. lysine intake resulted in estimates of availability similar to, or higher than, the slope-ratio analysis but was associated with greater statistical invalidity and higher standard deviations. 5. The proportion of energy retained in the carcasses was unaffected by the inclusion levels of lysine or soya-bean meal. Energy retention was depressed (P less than 0.05) with the three lupin-seed meals and the meat-and-bone meal. 6. In the second experiment, the response of pigs given a diet containing lupin-seed meal was inferior, on a carcass basis (P less than 0.05), to that of pigs given a diet containing soya-bean meal formulated to similar total lysine and digestible energy contents. 7. The addition of soya-bean oil to the diet containing lupin-seed meal, to equalize the estimated net energy of the diet to that of the diet containing soya-bean meal, depressed protein deposition (P less than 0.05) and increased fat deposition (P less than 0.05), indicating that energy was not limiting the growth of pigs given the lupin-seed-meal diet. 8. Autoclaving the lupin-seed at 121 degrees for 5 min had no effect on the growth of pigs, indicating that the low availability of lysine was not due to the presence of heat-labile anti-nutritional factors.

The analgesic effect, acute toxicity and pharmacokinetics of lysine acetylsalicylate (LAS), a water-soluble salt of acetylsalicylic acid (ASA) were studied as compared with a 50% solution of analgin and a 4% solution of amidopyrine at intramuscular administration and ASA administered intragastrically. During inflammation-induced pain in rats LAS exerts a pronounced analgesic effect exceeding the activity of other agents. LD50 of LAS was similar to that of analgin and ASA. LAS toxicity was significantly less than that of amidopyrine. Bioavailability of ASA at intramuscular administration to rabbits was close to that at intravenous injection and significantly higher as compared with intragastric administration.

Non-saturable penetration and the V and Km constants of saturable influx of leucine, lysine and glycine were always greater in cultured neuroblastoma (C1300) than in glioma (C6) cells. Aspartate uptake was detected only in glioma cells. Unstimulated efflux of the amino acids was initially fast in both cell types but soon slowed down. The efflux of glycine and aspartate exhibited no heteroexchange, the efflux of lysine was stimulated by extracellular leucine and that of leucine slightly by lysine and glycine but only in glioma cells.

Blood-brain barrier (BBB) function was assessed in 19-21-day-old rats exposed to low level lead from birth. Newborn rats received lead via milk from lactating dams given drinking water containing 0.1% lead acetate [Pb(Ac)2]. The treatment regime produced lead levels in the neonates within the range 20-80 micrograms dl-1 blood, without affecting growth. Cerebrovascular permeability (PS-product) to the diffusion-limited solute mannitol was unchanged in six regions of the cerebral hemisphere, the cerebellum and the brainstem, suggesting that barrier integrity was not affected by the low dose lead treatment. Regional cerebrovascular permeability to nutrient tracers representing seven BBB transport classes was not impaired by lead treatment. However, the PS estimates for the amino acids lysine and histidine and for thiamine were greater than control in some regions of the cerebral hemisphere. These alterations in nutrient supply to the brain may reflect altered substrate utilization associated with repair processes or delayed maturation of the CNS.

1. Utilisation of supplementary free L-lysine hydrochloride was estimated in growing chicks and compared to that of protein-bound lysine. The technique used is based on the oxidative catabolism of either free (U-14C)-L-lysine or the labelled lysine incorporated into yeast proteins. 2. The animals received a wheat-wheat gluten diet which was L-lysine-supplemented with either unlabelled yeast proteins or a mixture of synthetic amino acids simulating the yeast proteins or L-lysine hydrochloride alone. 3. At 13 and 15 days after hatching, expiry of (14C)--carbon dioxide was followed 8 h after dosing with the appropriate radiolabelled diet. After 4 h, 0.66% of the protein-bound and 5.3 to 5.7% of the free lysine radioactivity appeared as 14C--carbon dioxide. 4. It is concluded that under these conditions lysine from both sources was utilised more efficiently than had been assumed hitherto, protein-bound lysine being slightly better utilised than free lysine.

1. We have employed a paired-tracer isotope dilution technique in a perfused rat hindlimb preparation to obtain information on the kinetics of transport across the sarcolemmal membranes of acidic, neutral and basic amino acids. 2. We have defined the characteristics of the saturable transport of amino acids normally regarded as paradigm substrates for the A, ASC, L, y+(basic) and the dicarboxylic amino acid transport systems. Their maximal transport capacities (Vmax, nmol min-1 (g muscle)-1 and substrate concentrations for half-maximal transport (Km, mM) of representative amino acid substrates are as follows: 2-aminoisobutyrate (AIB), Vmax = 15 +/- 7, Km = 1.26 +/- 0.6; alanine, Vmax = 332 +/- 53, Km = 3.9 +/- 0.9; serine, Vmax = 410 +/- 61, Km 3.4 +/- 0.5; leucine, Vmax = 2800 +/- 420, Km = 20 +/- 2; lysine, Vmax = 136 +/- 46, Km = 2.1 +/- 1.3; glutamate, Vmax = 86 +/- 6, Km = 1.05 +/- 0.05; proline, Vmax = 196 +/- 48, Km = 4.1 +/- 0.6. 3. Glycine uptake was faster than expected on the basis of diffusion but was not saturable and showed uptake that could be best described by a first-order rate constant of 0.07 +/- 0.003 min-1. 4. We have attempted to discriminate kinetically between possible routes of entry for an amino acid on the basis of competitive and non-competitive interaction between substrates potentially sharing common routes. On this basis, the major routes of alanine entry appear to be via the ASC and L systems with the A system playing a quantitatively minor role. Glutamate and aspartate appear to be transported exclusively by a dicarboxylate amino acid carrier. The branched-chain amino acids (BCAA) and the aromatic amino acid, phenylalanine, are almost equivalent substrates for an L-like system. 5. Insulin had no detectable effect on the uptake of paradigm substrates for ASC, L, y+, the dicarboxylic amino acid or glycine transport systems. 6. Transport of serine and lysine was Na+ dependent. Lysine transport apparently occurred with a stoichiometry of 2 Na+: 1 lysine. With the exception of alanine, whose transport was partially Na+ dependent, all other amino acids examined in the present study were transported in a Na+-independent manner.

Renal tubular reabsorption of cystine and lysine were studied in the isolated perfused rat kidney to bridge the gap between in vivo clearance studies, and in vitro transport studies of tubule fragments, cells, and brush-border membranes. Lysine was reabsorped by a saturable transport system shared by the dibasics. Cystine was also reabsorbed by a saturable transport system, which was shared in part by the dibasics (maximum inhibition 30%). The lysine threshold (Fmin) was 0.9 mumol.min-1.g-1, with a tubular maximum (TM) of 2.4 mumol.min-1.g-1. The cystine Fmin was 0.06 mumol.min-1.g-1; the TM could not be estimated because it was above the limit of cystine solubility. There was no evidence of cystine "secretion." The gamma-glutamyltransferase inhibitor, AT-125, decreased cystine excretion, but only in the presence of glutathione, glycine, glutamate, and the diabasic amino acids. This suggests that cystine from glutathione degradation at the brush border may contribute to urinary cystine (an explanation of the phenomenon of cystine secretion), but only under certain conditions.

The pharmacokinetic profile of an innovative formulation of soluble aspirin (l-ornithine acetylsalicylate, ldB 1003) was compared with that of conventional tablets and two other soluble dosage forms (d, l-lysine acetylsalicylate and a buffered effervescent formulation of acetylsalicylic acid) after administration of single oral doses in six normal volunteers. All soluble forms showed a rapid absorption profile, peak plasma salicylic acid levels being attained after about 30 min on average and without statistically significant differences among the solutions tested. As compared to the soluble formulations, acetylsalicylic acid given as tablets resulted in slower absorption, with peak plasma salicylic acid levels being reached more than 1 h after dosing. Despite these differences in time course of plasma level profiles, the extent of absorption was similar for all formulations. Apart from the potential advantages in terms of improved gastric tolerability, the increased rate of absorption of aspirin solutions is therapeutically useful whenever a rapid onset of action is required. In this respect, the kinetic pattern of the innovative formulation compares favourably with that of other available soluble dosage forms.

1. The availability of lysine for pigs, rats and chicks was determined using samples of meat and bone meal (MBM) subjected to different pressure and temperature treatments during dry-rendering processing. The relation between slope-ratio estimates and three chemical tests for estimating 'available' lysine was assessed. 2. The availability of lysine (proportion of total) for pigs was 0.97 in the control. Pressure (275 kPa gauge, 141 degrees, for 30 min) in the early stage of rendering reduced availability to 0.74 and, in the late stage, to 0.46. Maintaining the final temperature at 125 degrees for 4 h had little effect (0.84) whereas a higher temperature of 150 degrees for 4 h reduced availability to 0.38. 3. Availability estimates for rats were lower than those of the pig, ranging from 0.88 in the control to 0.21 for the high-temperature treatment (150 degrees for 4 h). The effects for temperature were similar to those for the pig, whereas the effect of pressure was equally detrimental in both the early and late stages (0.45 and 0.43 respectively). 4. For chicks, availability estimates were similar to those for the pig for the control (0.93) and the two temperature treatments (0.86 and 0.31 for the 125 degrees and 150 degrees treatments respectively). The chick was less susceptible to the effect of pressure applied to the MBM (0.78 and 0.63 for the early- and late-stage treatments respectively). 5. Values for the indirect- and direct-1-fluoro-2,4-dinitrobenzene-(FDNB)-'available'-lysine assays decreased from 0.86 and 0.74 to 0.57 and 0.54 for the control and 150 degrees for 4 h treatments respectively, indicating that approximately half the reduced availability involved reactions with the epsilon-amino group of lysine. There was little relation between the FDNB values and lysine availability for the treatments involving changes in pressure. 6. There was little or no relation between dye-binding capacity of the meals, as assessed by the Acid Orange-12 dye-binding procedure (Hurrell et al. 1979), and lysine availability for the three species.

1. The initial rate of L-lysine influx into erythrocytes from 13 patients with chronic renal failure has been measured using 14C-labelled lysine. Ten patients were on maintenance haemodialysis and three had never been dialysed. The results are compared with data obtained from 12 normal individuals. 2. The rate of lysine influx into washed cells from buffered saline containing 0.02-0.5 mmol of L-lysine/l has been calculated. The results can be fitted with a model in which influx has a single saturable component obeying Michaelis-Menten kinetics, and a linear non-saturable component. 3. In uraemic erythrocytes the saturable component had a mean Vmax. of 0.762 mmol h-1 litre-1 of cells (n = 13, SEM 0.072) and a mean Km of 68.2 mumol/l (SEM 5.7). These values in normal erythrocytes were 0.566 mmol h-1 litre-1 of cells (n = 12, SEM 0.033) and 70.5 mumol/l (SEM 4.1), respectively. The mean apparent diffusion constant (KD) for the linear component of influx was 0.224 h-1 (SEM 0.039) in uraemic cells and 0.178 h-1 (SEM 0.028) in normals. 4. The 35% increase in mean Vmax seen in uraemic erythrocytes was statistically significant (P = 0.02). A similar increase in Vmax. in uraemic cells compared with controls was seen in erythrocytes which were studied in zero-trans conditions after depletion of intracellular amino acids. The mean values of Km and KD were not significantly different in uraemia. The origins of this increased membrane transport capacity for lysine in uraemia are discussed.

The characteristics of L-lysine transport were investigated at brush-border (maternal) and basal (fetal) sides of the syncytiotrophoblast in the term guinea-pig placenta artificially perfused either through the umbilical vessels in situ or through both circulations simultaneously. Cellular uptake, efflux and transplacental transfer were determined using a single-circulation paired-tracer dilution technique. Unidirectional L-[3H]lysine uptake (%) (perfusate lysine 50 microM) was high on maternal (M = 87 +/- 1) and fetal (F = 73 +/- 2) sides. L-[3H]Lysine efflux back into the ipsilateral circulation was asymmetrical (F/M ratio = 2.3) and transplacental flux occurred in favour of the fetal circulation. Unidirectional lysine influx kinetics (0.05-8.00 mM) gave Km values of 1.75 +/- 0.70 mM and 0.90 +/- 0.25 mM at maternal and fetal sides, respectively; corresponding Vmax values were 1.95 +/- 0.38 and 0.87 +/- 0.10 mumol.min-1.g-1. At both sides, lysine influx (50 microM) could be inhibited (about 60-80%) by 4 mM L-lysine and L-ornithine and less effectively (about 10-40%) by L-citrulline, L-arginine, D-lysine and L-histidine. At the basal side: (i) lysine influx kinetics were greatly modified in the presence of 10 mM L-alanine (Km = 6.25 +/- 3.27 mM; Vmax = 2.62 +/- 0.94 mumol.min-1.g-1), but unchanged by equimolar L-phenylalanine or L-tryptophan; (ii) in the converse experiments, lysine (10 mM) did not affect the kinetic characteristics for either L-alanine or L-phenylalanine; (iii) L-lysine and L-alanine influx kinetics were not dependent on the sodium gradient; (iv) the inhibition of L-[3H]lysine uptake by 4 mM L-homoserine was partially (60%) Na+-dependent. At the maternal side the kinetic characteristics for alanine influx were highly Na+-dependent, while lysine influx was partially Na+-dependent only at low concentrations (0.05-0.5 mM). Bilateral perfusion with 2,4-dinitrophenol (1 mM) reduced L-[3H]lysine uptake into the trophoblast and abolished transplacental transfer. It is suggested that lysine transport in the guinea-pig placenta is mediated by a specific transport system (y+) for cationic amino-acids. The asymmetry in the degree of sodium-dependency at both trophoblast membranes may in part explain the maternal-to-foetal polarity of placental amino-acid transfer in vivo.

Preincubation of resting cells of Saccharomyces cerevisiae double mutant can1 gap1 (with a single transport system for L-lysine) with metabolic substrates stimulated subsequent uptake of lysine. While in the wild type the stimulation is connected primarily with carrier protein synthesis (delayed, cycloheximide-inhibitable effect) in the mutant an immediate tapping of an energy source (antimycin-inhibited) is practically solely involved.

The uptake of biotin and biocytin was investigated in rat intestine using the everted sac technique. It has been shown that at biotin and biocytin concentrations less than 40 and 50 nM respectively, absorption proceeds by a saturable process, whereas at higher concentrations uptake by passive diffusion predominates. Fractionation of solubilized brush border preparations indicates that biotinidase is the only protein which binds biotin in this preparation.

The intestinal absorption of lysine and arginine in the chick was characterized using an in situ-ligated intestinal segment technique, and the influence of dietary electrolytes on their absorption was examined. Each amino acid, labeled with 14C and provided at a concentration of .5 mM, was introduced into the lumen of the small intestine of young chicks. Absorption was defined as disappearance of label from the lumen after 4 min. Lysine absorption was greater than arginine absorption in the duodenum and in the middle and distal small intestine. The Jmax values for absorption of lysine and arginine were 315.0 nmol/min and 112.0 nmol/min, whereas the respective Kt values were 2.3 mM and 2.0 mM. Maximal transport of lysine and arginine occurred at pH 6.0. Lysine absorption was depressed (P less than .05) at pH 5.0 and pH 8.0, whereas arginine absorption was depressed (P less than .05) only at pH 8.0. High dietary chloride (.89%) produced higher (P less than .05) lysine absorption than a high dietary level of potassium (1.81%). No effect (P greater than .05) of dietary electrolytes on arginine absorption was detected. These results indicate that the dietary balance of monovalent electrolytes, and, hence, acid-base balance, may influence the intestinal absorption of lysine.

Brush border membrane vesicles (BBMV) were prepared from the gills of the marine mussel, Mytilus edulis. These membranes contained two distinct pathways for cotransport of Na+ and alpha-neutral amino acids. The major pathway in mussel gill BBMV was the alanine-lysine (AK) pathway, which had a high affinity for alanine and for the cationic amino acid, lysine. The AK pathway was inhibited by nonpolar alpha-neutral amino acids and cationic amino acids, but was not affected by beta-neutral amino acids or imino acids. The kinetics of lysine transport were consistent with a single saturable process, with a Jmax of 550 pmol/mg-min and a Kt of 5 microM. The AK pathway did not have a strict requirement for Na+, and concentrative transport of lysine was seen in the presence of inwardly directed gradients of Li+ and K+, as well as Na+. Harmaline inhibited the transport of lysine in solutions containing either Na+ or K+. The alanine-proline (AP) pathway transported both alanine and proline in mussel gill BBMV. The AP pathway was strongly inhibited by nonpolar alpha-neutral amino acids, proline, and alpha-(methylamino)isobutyric acid (Me-AIB). The kinetics of proline transport were described by a single saturable process, with a Jmax of 180 pmol/mg-min and Kt of 4 microM. In contrast to the AK pathway, the AP pathway appeared to have a strict requirement for Na+. Na+-activation experiments with lysine and proline revealed sigmoid kinetics, indicating that multiple Na+ ions are involved in the transport of these substrates. The transport of both lysine and proline was affected by membrane potential in a manner consistent with electrogenic transport.