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The effects of dietary saturated and polyunsaturated fat on the metabolism of apolipoprotein A-I (apoA-I) and apolipoprotein B (apoB) were studied in a patient with type IIb hyperlipoproteinaemia. On the saturated fat diet, the rate of synthesis of very low density lipoprotein apoprotein B (VLDL-apoB) was approximately twice normal, accounting for the increased plasma VLDL pool in this subject. However, 54% of the synthesized VLDL-apoB was catabolized by a pathway independent of low density lipoproteins (LDL). The metabolic conversion rate of VLDL-apoB to LDL-apoB was normal in this subject and his expanded plasma LDL-apoB pool resulted, not from increased input of the apoprotein from VLDL, but from a decrease in its fractional clearance rate. On the polyunsaturated diet, there was a significant fall in the plasma cholesterol and triglyceride concentrations and a change in the fatty acid composition of all plasma lipoprotein fractions. These changes were accompanied by a decrease in the plasma concentrations of apoA-I and apoB which resulted from a reduction of apoprotein synthetic rate.

The activities of jejunal carbohydrate-metabolizing enzymes show adaptive changes in response to dietary substances, drugs, and sex hormones. To learn whether insulin, tolbutamide, and glucagon had effects on these enzymes, we performed serial peroral jejunal biopsies in normal young men and in obese patients, before and after treatment with these agents. Jejunal mucosa was assayed for glycolytic enzyme activities, pyruvate kinase (PK), hexokinase (HK), and fructose-1,6-diphosphate aldolase (FDPA), and the nonglycolytic enzyme activity, fructose diphosphatase (FDPase). Insulin significantly increased the activity of jejunal PK (+48% change from control) and HK (+6%), decreased the activity of FDPase (−36%), and had no effect on FDPA. Glucagon had opposite effects; the activity of PK was decreased (−33%) and FDPase was increased (+50%). Tolbutamide significantly increased the activities of PK (+47%), HK (+14%), and FDPA (+7%), and decreased the activities of FDPase (−36%). The results suggest that at least some of the effects of tolbutamide on glycolytic enzyme activities were independent of endogenous insulin. The data support the concept that jejunal carbohydrate-metabolizing enzymes in man respond to hormones and drugs similar to responses observed in rat liver. This is important because it now gives us a means of studying the actions of these hormones directly in human tissue.

Apolipoprotein-serine (apoLP-Ser or apoC-I) is one of the apoprotein constituents of human plasma very low density lipoprotein. The protein has 57 amino acid residues, including one residue of methionine and is lacking histidine, cysteine, cystine, and tyrosine. The NH2 terminus of apoLP-Ser is threonine and the COOH terminus is serine. Cleavage of apoLP-Ser with cyanogen bromide, followed by chromatography of the digest on Bio-Gel P-30 in 25% formic acid, yielded two fragments corresponding to the NH2-terminal (CNBr I) and the COOH-terminal (CNBr II) fragments and accounting for the 57 residues of the intact protein. The amino acid sequences of the tryptic peptides from CNBr I and chymotryptic peptides from CNBr II were determined by conventional methods. The amino acid sequence of apoLP-Ser is as follows: Thr-Pro-Asp-Val-Ser-Ser-Ala-Leu-Asp-Lys-Leu-Lys-Glu-Phe-Gly-Asn-Thr-Leu-Glu-Asp-Lys-Ala-Arg-Glu-Leu-Ile-Ser-Arg-Ile-Lys-Gln-Ser-Glu-Leu-Ser-Ala-Lys-Met-Arg-Glu-Trp-Phe-Ser-Glu-Thr-Phe-Gln-Lys-Val-Lys-Glu-Lys-Leu-Lys-Ile-Asp-Ser.

Radioiodinated human apolipoprotein A-I, when incubated with plasma lipoproteins, associates exclusively with high density lipoproteins. It does not interact with very low density lipoproteins or low density lipoproteins. Binding is rapid, being complete within 10 min, and is not affected by variation of pH within the range 6.0–9.5 or of temperature over the range 0°–37°C. At equimolar concentrations of apolipoprotein A-I and high density lipoproteins, 0.58 mol of the apoprotein bind per mol of high density lipoproteins. Binding increases progressively with apolipoprotein A-I concentration up to an apolipoprotein A-I : high density lipoprotein molar ratio of 20 : 1, when each mol of lipoprotein binds 7.62 mol of apoprotein. Interaction of apolipoprotein A-I with high density lipoproteins displaces endogenous apolipoprotein A-I from the particle to a maximum of 2 mol of apolipoprotein A-I per mol of high density lipoproteins. This displacement occurs at an apoprotein : lipoprotein molar ratio of 10 : 1. The rest of the endogenous apolipoprotein A-I is not displaceable, even when the exogenous apoprotein : lipoprotein ratio is increased to 20 : 1. Incubation of apolipoprotein A-I and high density lipoproteins at molar ratios of 0.3 or less results in a mol for mol exchange of exogenous with endogenous apolipoprotein A-I on the lipoprotein. The half-life of 131I-labeled apolipoprotein A-I/high density lipoproteins in rats and rabbits is 15 h and 1.40 days respectively; the material decays exponentially from the bodies of these animals. More than 94% of the radioactivity in their plasma is associated with a component of hydrated density 1.063–1.21 kg/l. When injected into humans, the radioiodinated apoprotein incorporated into high density lipoproteins by in vitro incubation is cleared from the plasma 20% faster than endogenous apolipoprotein A-I in high density lipoproteins.

Insulin and glucagon injected into the portal vein produced rapid reciprocal changes in the activities of certain hepatic glycolytic enzymes and fructose diphosphatase in the rat. Insulin produced a rapid increase in hepatic phosphofructokinase and pyruvate kinase activities and a decrease in fructose diphosphatase activity. Glucagon produced a rapid but reciprocal response in each of these enzyme activities. Fructose diphosphate aldolase activity was unaltered by either hormone. The insulin effect on these enzymes was detected within 5 min following injection, was maximal by 10 min, and then gradually declined over the remaining 30 min of testing. The magnitude of the insulin effect was dependent on the amount of insulin injected. No effect was detected when 0.005 unit per kg (0.001 unit) was injected; phosphofructokinase and pyruvate kinase activities were slightly increased with 0.015 unit per kg (0.003 unit); phosphofructokinase, pyruvate kinase, and fructose diphosphatase activities were altered with 0.15 unit per kg (0.03 unit) and 1.5 units per kg (0.3 unit), with the higher dose giving a slightly greater effect. The insulin effect was not associated with a significant change in cyclic adenosine 3':5'-monophosphate concentrations. The glucagon effect on the enzyme activities was preceded by a significant increase in cyclic adenosine 3':5'-monophosphate concentrations, which occurred within 30 s after hormone injection. A change in enzyme activities was found at 2 to 5 min and was maximal 5 to 10 min following glucagon injection. The hormone effect on enzyme activities and cyclic adenosine 3':5'-monophosphate levels was dependent on the amount of glucagon injected, being maximal at doses of 150 to 300 µg. Pretreatment of the rat with actinomycin D or puromycin did not alter the response of the enzymes to insulin and glucagon, indicating that de novo protein synthesis was not responsible for the change in enzyme activities. Glucagon injected 5 min following insulin reversed the insulin effect; insulin given 5 min after glucagon also partially reversed the glucagon effect on cyclic adenosine 3':5'-monophosphate and the enzyme activities. Intravenous insulin produced rapid changes in the activities of renal cortical, skeletal muscle, and epididymal fat glycolytic enzymes and fructose diphosphatase in the rat. Insulin (0.15 unit per kg) produced rapid increases in pyruvate kinase and phosphofructokinase and rapid decrease in fructose diphosphatase activities in all tissues. Fructose diphosphate aldolase activity was unchanged following insulin infusion. Intravenous glucagon (0.15 mg) produced rapid changes, reciprocal to those seen with insulin, in fructose diphosphatase activity in all tissues. Glucagon significantly decreased epididymal fat phosphofructokinase activities but did not alter the activity of this enzyme in the renal cortex and skeletal muscle. Glucagon significantly decreased renal cortical pyruvate kinase but had no effect in the epididymal fat and skeletal muscle. Fructose diphosphate aldolase activity was unchanged in all tissues following glucagon infusion. Cyclic adenosine 3':5'-monophosphate infusion (0.05 mmole) produced significant changes in pyruvate kinase, phosphofructokinase, and fructose diphosphatase activities in all tissues which resembled those changes seen following glucagon infusion. These data suggest that the glucagon responses seen in the four tissues studied are mediated by cyclic adenosine 3':5'-monophosphate.

Epinephrine infusion into the portal vein produced rapid changes in the activities of certain hepatic, epididymal fat, and skeletal muscle glycolytic enzymes and fructose diphosphatase in the rat. Epinephrine produced a rapid increase in hepatic, epididymal fat, and skeletal muscle fructose diphosphatase activity. In contrast, epinephrine produced a rapid decrease in hepatic phosphofructokinase, pyruvate kinase, and glucokinase activities. Epinephrine also lowered skeletal muscle phosphofructokinase and pyruvate kinase activities. However, epinephrine had no significant effect upon epididymal fat pyruvate kinase and phosphofructokinase activities. Fructose diphosphate aldolase activities were unchanged in the liver, epididymal fat, and skeletal muscle. The epinephrine effect on the hepatic enzymes was maximal within 2 to 5 min following injection of 2 µg and then gradually returned to control levels over the remaining 35 to 38 min of testing. The magnitude of the epinephrine effect was dose-dependent. No effect was detected when 0.25 µg per min was injected. Phosphofructokinase, pyruvate kinase, and fructose diphosphatase activities were significantly altered at a dose level of 1.0 µg per min, with maximal changes occurring at the 2.0- to 4.0-µg per min dose level. The epinephrine effect was associated with a significant increase in hepatic cyclic adenosine 3′:5′-monophosphate concentrations. Actinomycin D and puromycin treatment did not alter the response of the enzymes to epinephrine. Insulin given 5 min following epinephrine partially reversed the epinephrine effect. Similarly, epinephrine given 5 min following insulin partially reversed the insulin effect. We suggest that the epinephrine effect is mediated through cyclic adenosine 3′:5′-monophosphate and may be due to phosphorylating mechanisms analogous to that responsible for the regulation of glycogen metabolism.

1. 1. Low density lipoproteins (LDL) were isolated from pig plasma by ultracentrifugal flotation in KBr between densities 1·020 and 1·060 g/ml (LDL 1 ) and between 1·060 and 1·090 g/ml (LDL 2 ). 2. 2. The chemical, immunological and physical properties of LDL 1 and LDL 2 were compared with each other and with human LDL. 3. 3. LDL 1 and LDL 2 were delipidated and fractionated by chromatography on Sephadex G-150 in 0·1 M Tris-HC1, pH 8·0, containing 2 mM sodium decyl sulfate. ApoLDL 1 and apoLDL 2 were immunochemically identical, had only minor differences of amino acid composition and had indistinguishable circular dichroic spectra. The apoproteins were very similar in amino acid composition and circular dichroic spectra to human apoLDL. 4. 4. Our findings strongly suggest that the apoproteins from pig LDL 1 and LDL 2 are identical and that this protein is similar but not identical to apoLDL from man.

The relative toxicity and metabolic effectiveness of cholecalciferol (CC) and 25-hydroxycholecalciferol (25-HCC) in chicks were evaluated by feeding six graded levels of each and observing gross and microscopic pathology as well as several metabolic parameters of calcium metabolism. Renal tubular calcification was observed when CC was fed at the rate of 10.0 mg/kg of diet and when 25-HCC was fed at the rate of 0.1 mg/kg diet. Thus, 100-fold increase in toxicity results when the hydroxylated form of CC is fed. Both microscopic renal lesions and increased renal calcium and inorganic phosphate concentrations occurred in chicks with normal serum calcium concentrations.

High density lipoproteins (HDL) were isolated from pig plasma by ultracentrifugal flotation between densities 1.063 and 1.210 g per ml. After delipidation, the apolipoproteins were fractionated by chromatography on Sephadex G-150 and DEAE-cellulose in 5.4 m urea. One major apolipoprotein was isolated and characterized. From its chemical and physical properties, this major apolipoprotein appears very similar to apoLP-Gln-I from human HDL. Pig HDL appears to differ from human HDL in a marked decrease in the relative content of apoLP-Gln-II in the pig lipoprotein family. A distinct peak associated with apoLP-Gln-II was not identified by chromatography of pig apoHDL. A small quantity of a protein with the same mobility of human apoLPGln-II was detected in pig apoHDL after polyacrylamide gel electrophoresis in sodium dodecyl sulfate. The major apolipoprotein from pig HDL had an approximate molecular weight of 26,000 as determined by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. Its calculated molecular weight from amino acid analysis was 29,800. Rabbit antisera prepared against the pig apolipoprotein formed precipitin lines of partial identity between this protein and apoLP-Gln-I from human HDL. Treatment of the pig apolipoprotein with carboxypeptidase established Leu-Gln as the COOH-terminal sequence. Pig and human apoLPGln-I had similar amino acid compositions, but the pig protein contained isoleucine and had 12 more residues of alanine than did human apoLP-Gln-I. Pig and human apoLP-Gln-I had indistinguishable absorption spectra and similar circular dichroism spectra indicating a relatively high content of α-helical conformation. Both proteins activated human lecithin : cholesterol acyltransferase. These studies demonstrate that the major apolipoprotein from human and pig HDL have similar chemical, immunological, physical, and physiological properties.