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(Co beta-5'-Deoxyadenosin-5'-yl)-(p-cresolyl)cobamide (Ado-PCC), an analogue of the base-off form of coenzyme-B12 (CoB12), was prepared by alkylation of (Co alpha/beta-cyano/aqua)-(p-cresolyl)cobamide (PCC) with 5'-chloro-5'-deoxyadenosine. The 500 MHz 1H-NMR spectrum of Ado-PCC in D2O at pH 7.4 was completely analyzed using COSY and NOESY two-dimensional experiments. The coenzyme and inhibitory activities of Ado-PCC were tested with three coenzyme-B12-dependent enzymes: (R)-methylmalonyl-CoA mutase, glycerol dehydratase, and diol dehydratase. Ado-PCC showed strong coenzyme activity with methylmalonyl-CoA mutase, which is known to bind the base-off form of CoB12. In contrast, Ado-PCC had no coenzyme activity but acted instead as a competitive inhibitor with glycerol dehydratase and diol dehydratase, which are likely to prefer the base-on form of CoB12. These results indicate that Ado-PCC, whose structure is analogous to the base-off form of CoB12, can be used for probing the mode of coenzyme binding by coenzyme-B12-dependent enzymes.

1. [4-13C]Nicotinate was synthesised and used to support the growth of a nicotinate auxotrophic mutant of Pseudomonas putida. 13C-NMR spectroscopy of the isolated urocanase confirmed the efficient incorporation of 13C into C4 of the nicotinamide ring of the tightly bound NAD+ cofactor. 2. beta-[( 2'-13C]Imidazol-4-yl)propionate was synthesised according to known procedures and used for inhibition of the 13C-labelled urocanase. An increase in the absorbance at 330 nm indicated adduct formation between enzyme-bound NAD+ and inhibitor. The adduct was stabilised by oxidation with phenazine methosulfate and isolated using a slight modification of the procedure of Matherly et al. [Matherly, L. H., DeBrosse, C. W. & Phillips, A. T. (1982) Biochemistry 21, 2789-2794]. 3. The 13C-NMR spectrum of the doubly labelled adduct, [4-13C]NAD-[2'-13C]imidazolylpropionate, showed no one-bond 13C-13C coupling between labelled sites. The 1H-NMR spectrum of this adduct in 2H2O showed only one imidazole signal, which appeared as a doublet (1JC-H = 212 Hz), confirming the presence of a proton at the labelled C2'. The lack of a C5' signal and further NMR data provide evidence for a C-C bond between C4 of the nicotinamide and C5' of the imidazole ring. 4. The revised structure for the enzymatically formed addition complex suggests a novel mechanism for the urocanase reaction which is not only chemically plausible but also explains the previously observed urocanase-catalysed exchange of the C5 proton of urocanate and of beta-(imidazol-4-yl)propionate.

The synthetic D-galactose analog 2-deoxy-2-fluoro-D-galactose (dGalF) offers unique advantages for studies of the D-galactose pathway by non-invasive techniques using 19F-NMR spectroscopy or positron emission from the 18F-labeled compound. The metabolism of 2-deoxy-2-fluoro-D-galactose was studied in rodents using the unlabeled, the 18F-labeled, and the 14C-labeled D-galactose analog. Analyses for the metabolites of 2-deoxy-2-fluoro-D-galactose were performed by HPLC, enzymatic methods, and 19F-NMR spectroscopy in vivo and in vitro. The metabolism of 2-deoxy-2-fluoro-D-galactose was most active in the liver which took up the major part of the administered dose of the 14C-labeled D-galactose analog, but renal excretion was also pronounced. This was confirmed by in vivo scanning of the rat using the 18F-labeled sugar (1.5 microCi/g; 25 nmol/g) and examination by positron-emission tomography and gamma camera. The dose dependence of the levels of the hepatic metabolites of 2-deoxy-2-fluoro-D-galactose was investigated for doses between 25 nmol/g body mass and 1 mumols/g body mass. After 1 h, the major part of the acid-soluble uracil nucleotides consisted of UDP-2-deoxy-2-fluoro-D-hexoses when the dose was at least 0.1 mumols/g. With higher doses, 2-deoxy-2-fluoro-D-galactose 1-phosphate became the predominant initial metabolite. After a dose of 1 mumols/g 2-deoxy-2-fluoro-D-galactose 1-phosphate accumulated rapidly (5.3 +/- 0.4 mumols/g liver after 30 min) followed by the formation of UDP-2-deoxy-2-fluoro-D-galactose and UDP-2-deoxy-2-fluoro-D-glucose (0.7 +/- 0.1 mumols/g and 1.8 +/- 0.1 mumols/g, respectively, after 5 h). The diversion of uridylate, due to the accumulation of UDP-2-deoxy-2-fluoro-D-hexoses, was associated with a rapid depletion of hepatic UTP, UDP-glucose, and UDP-galactose. The UTP content was decreased to 11 +/- 6% of normal within 15 min after administration of 2-deoxy-2-fluoro-D-galactose at a dose of 1 mumols/g. The UTP-depleting action was minimal, however, at a dose of 25 nmols/g or less, indicating that interference in uridylate metabolism would be negligible at the doses required for positron-emission tomography of the liver using the 18F-labeled compound. At higher doses, the UTP deficiency induced by 2-deoxy-2-fluoro-D-galactose could be useful in the chemotherapy of D-galactose-metabolizing tumors such as hepatocellular carcinoma.(ABSTRACT TRUNCATED AT 250 WORDS)

Longitudinal and transverse relaxation times were measured for well-resolved and assigned methyl proton resonances of erabutoxin b at 270 MHz, 300 MHz and 500 MHz. Both longitudinal and transverse magnetization decay curves are non-exponential due to cross-relaxation and cross-correlation effects. The longitudinal and transverse relaxation rates were obtained from the initial slope of both magnetization decay curves. The correlation times for the isotropic tumbling motion of the protein were determined to be 2.82 ns at 300 K and 1.62 ns at 330 K from the analysis of the relaxation data of some alpha protons. Using these values, the relaxation data of methyl protons were fitted to various theoretical models. Most of the methyl resonances could be fitted well to a model which allowed methyl rotation (in the range 0.01-0.05 ns) and an external contribution from protons assumed to be in positions derived from X-ray coordinates. The data for a few methyl groups, however, could not be fitted in this way. For these a smaller number of external protons than predicted by the X-ray coordinates was assumed. Additionally, a larger amplitude motion had to be introduced into the model for particular residues. This additional motion requires concerted protein motion close to these residues, since the X-ray structure suggests that steric hindrance would prevent local motion. These results are consistent with the idea of a flexible and dynamic structure for proteins.

Binding of the lac repressor headpiece, the N-terminal region of the lac repressor, to the lac operator of Escherichia coli was studied by 1H-NMR spectroscopy. Two DNA fragments, of 51 base pairs and 62 base pairs, containing the lac operator region, were investigated. The signals of their hydrogen-bonded imino protons were well resolved in the 500-MHz NMR spectra. The spectra of the free lac operator DNA are similar to those obtained from ring-current-shift calculations for a B-DNA structure. Complex formation with the headpiece led to small but nevertheless characteristic changes in the spectra. The fact that very few imino resonances shifted upon addition of headpiece, as well as the variety in direction and size of these chemical shifts, indicate the formation of a specific complex between the lac repressor and the lac operator. The observed changes in the resonance positions exclude the intercalation of tyrosine residues of the headpiece between adjacent base pairs of the lac operator as well as the formation of a cruciform structure. They rather reflect a small conformational transition in the DNA itself, caused for example by an alteration in the tilt of a few base pairs or a shift of the keto-enol tautomeric equilibrium of the bases towards the enolic form.

The structure of carbohydrate units of bronchial-mucus glycoproteins obtained from cystic fibrosis patients was investigated by 500-MHz 1H-NMR spectroscopy and methylation analysis. To that purpose, the mucin was subjected to alkaline borohydride degradation. Neutral oligosaccharide-alditols, ranging in size from disaccharides to pentasaccharides, were isolated. Eight compounds could be purified to homogeneity; furthermore, three fractions were obtained consisting mainly of two components. For all 14 compounds the primary structure could be elucidated. 500-MHz 1H-NMR spectroscopy was found to be effective in detecting heterogeneity and to be invaluable for the determination of structures in mixtures of oligosaccharide-alditols. The structures can be divided into two groups depending on the core disaccharide. One group contains Gal(beta 1 leads to 3)GalNAc-ol as common structural element, the other GlcNAc(beta 1 leads to 3)GalNAc-ol. Both disaccharides were identified as such; the other compounds can be conceived as extensions thereof. The most complex representatives of the two groups are: (formula; see text) The italicized structural elements, comprising the SSEA-1 determinant and the type-1 blood-group-H determinant, are novel sequences in oligosaccharide chains of mucin-type glycoproteins.

1. By 1H nuclear magnetic resonance spectroscopy it has been shown that phenylpyruvate tautomerase from beef kidney catalyses the stereospecific exchange of one of the enantiotopic 3H-atoms in the side-chain of the substrate with solvent protons, the rate of spontaneous exchange being slow under physiological conditions. 2. Using monodeuterated phenylpyruvate of known absolute configuration it has been shown that the tautomerase removes specifically the 3-pro-R hydrogen atom of the substrate. 3. The circular dichroism spectra of the two enantiomeric 3-phenyl-[3-2H]pyruvates have been determined. 4. Some implications of these findings for the investigation of the metabolism of aromatic amino acids are discussed.

1. Samples of methylmalonyl-CoA and (2H3)methylmalonyl-CoA were prepared by a combination of chemical and enzymic methods. After ion-exchange chromatography the unlabelled methylmalonyl-CoA was pure, the deuterated substance contained 11-12% dephospho-CoA derivative. 2. The sample of unlabelled methylmalonyl-CoA was incubated in deuterated buffer with catalytic amounts of methylmalonyl-CoA mutase, epimerase, and coenzyme B12. The progress of the reaction was monitored directly by 1H-NMR spectroscopy at 500 MHz. After equilibrium was established, a slow mutase-catalysed deuterium incorporation into migratable positions of succinyl-CoA was observed. 3. The sample of (2H3)methylmalonyl-CoA was incubated in unlabelled buffer with a mixture of methylmalonyl-CoA mutase, epimerase and coenzyme B12. In withdrawn aliquots, the reaction was interrupted by acidification and the lyophilised samples were examined by 1H-NMR spectroscopy in deuterium oxide. Both rearrangement and protium incorporation into migratable positions of succinyl-CoA were monitored. 4. At comparable methylmalonyl-CoA to succinyl-CoA conversion rates, deuterium loss from migratable positions was 4-6 times faster than the corresponding protium loss. It is confirmed that the stereochemical error of the mutase is amplified by isotope discrimination when deuterium is in migratable positions, whereas it is diminished when protium is in migratable positions.

1. (5'R)-(5'-2H1)Adenosine [(5'R):(5'S) = 85:15] was prepared by a procedure which involved inter alia the reduction of 6-N-benzoyl-2',3'-O-isopropylidene-5'-oxoadenosine with a reagent obtained from LiAl2H4 and (-)-isoborneol. 2. (5'S)-(5'-2H1)AdoCbl [(5'S):(5'R) = 74:26] (AdoCbl = 5'-deoxyadenosylcobalamin) was synthesized by reacting cobal(I)amin with (5'R)-2'-3'-O-isopropylidene-5'-tosyl-(5'-2H1) adenosine followed by acid hydrolysis to remove the isopropylidene protective group. 3. (5'R)-(5'-2H1)AdoCbl [(5'R):(5'S) = 77:23] was prepared by reacting cobalt(I)amin with (5'S)-5'-chloro-5'-(5'-2H1)deoxyadenosine [(5'S):(5'R) = 80:20] obtained in turn from (5'R)-(5'-2H1)adenosine. The reaction sequence involved two consecutive inversions at the C-5' atom of adenosine 4. Comparison of the 500-MHz 1H-NMR spectra of unlabelled, (5'S)- and (5'R)-(5'-2H1)AdoCbl allowed assignment of the triplet at 0.58 ppm and the doublet at 1.525 ppm to the diastereotopic 5'-HRe and 5'-HSi atoms, respectively. On acidification, these two protons gave rise to two triplets at 0.11 ppm and 1.78 ppm indicating that torsion had occurred around the C-4'--C-5' bond. 5. Samples of (5'R)- and (5'S)-(5'-2H1)AdoCbl were incubated with methylmalonyl-CoA mutase from Propionibacterium shermanii. Examination by 1H-NMR spectroscopy at 500 MHz revealed partial loss and stereochemical scrambling of the deuterium at the 5' position. This indicates transient conversion of the C-5' atom into a torsiosymmetric group and hence cleavage of the cobalt-carbon bond during interaction with the enzyme. The mechanism by which deuterium is lost remains to be elucidated.

1. Starting from trans-cinnamic acid a chiral (-)3-phenyl-[2,3-2H]propionic acid has been synthesized using Clostridium kiuyveri cells as catalyst. 2. The chiral dideuterated acid has been converted by chemical methods to a mixture of (2R) and (2S)-phenyl[2,3-2H]-alanine. 3. By means of 1H nuclear magnetic resonance spectroscopy and the action of D and L-amino acid oxidase the configuration of the phenylalamine has been shown to be (2R, 3S) and (2S, 3S), respectively. The labelled phenylalanine is thus sterically and isotopically homogenous at position 3 but heterogenous at position 2.

The primary sequence Arg-Gly-Asp has been found in a number of proteins which bind to cell surface receptors. Studies with synthetic peptides have shown that the presence of charged side chains alone is not sufficient to confer binding activity. Application of folding algorithms to proteins and peptides having similar sequences indicates that binding activity is strongly correlated with the presence of two or more closely spaced residues that each have a high probability of initiating a beta-bend. Circular dichroic studies on the hexapeptide GRGDSP, whose sequence is contained in fibronectin and which also shows binding activity, demonstrate that it adopts an unusual conformation in aqueous solution. 1H-NMR spectra of the peptide in aqueous solution show that the two amide hydrogens of Asp4 and Ser5 exchange very slowly. Computer-assisted modeling using restrained molecular dynamics and energy minimization results in conformations that include two beta-bends of type III-III or III-I (hydrogen bonds 4----1 and 5----2), fully consistent with constraints imposed by 1H- and 13C-NMR data. It is suggested that this unusual secondary structure provides an additional specificity determinant.

When (methyl-2H3)methylmalonyl-CoA was reacted with partially purified methylmalonyl-CoA mutase, 1H-NMR revealed that about 24% of the migrating deuterium was lost after 88% conversion. When [methyl-3H]methylmalonyl-CoA was incubated with highly purified methylmalonyl-CoA mutase, tritium exchange with the medium depended on added methylmalonyl-CoA epimerase. With highly purified preparations of methylmalonyl-CoA mutase, effective tritium exchange from [5'-3H]adenosylcobalamin to water required the addition of methylmalonyl-CoA epimerase and of substrate (e.g. succinyl-CoA). By addition of [14C]succinyl-CoA to a partially purified preparation of methylmalonyl-CoA mutase, it was shown that the mutase binds one substrate molecule very tightly. Coupling the mutase reaction with the transcarboxylase reaction and using variously labelled succinyl-CoA as substrate, revealed that only (2R)- and not (2S)-methylmalonyl-CoA will be formed by the mutase with a kinetic isotope effect of 3.5 using (2H4)succinyl-CoA. When (1-13C) propionyl-CoA was reacted with a mixture of highly purified methylmalonyl-CoA carboxylase, epimerase and mutase, 13C-NMR signals were obtained for the thioester carbonyl of succinyl-CoA (relative intensity 100%) and of methylmalonyl-CoA (5%) as well as for the carboxyl of free succinic acid (27%) and of succinyl-CoA (less than 4.5%). Thus very little, if any, migration of the CoA from one carboxyl to the other appears to take place. (1,4-13C2)Succinic acid and (1,4-13C2)succinyl-CoA were synthesised and their 13C-NMR chemical shifts were exactly determined. Evidence is provided for a strict stereospecificity of the mutase toward the (2R)-epimer of methylmalonyl-CoA and for an incomplete stereospecificity toward the two diastereotopic 3-H atoms of succinyl-CoA. The latter, combined with a high intramolecular isotope discrimination, causes rapid washing-out of the migrating 2H and 3H to water and slow washing-in from the medium. Whenever migration of protium from the sterically less preferred 3-pro(S)- position of succinyl-CoA occurs and simultaneously a heavy isotope is maneuvered from the migratable 3-pro(R)- position into the labile alpha-position of methylmalonyl-CoA, the substitution by the COSCoA group takes place with inversion of configuration. When the sterically preferred 3-pro(R)-hydrogen atom migrates, the previously reported stereochemical retention occurs. A mechanistic and stereochemical scheme is discussed that fully accounts for all observations.

Starting from (13C)formic acid, acetone and cyanoacetamide samples of (4-13C)nicotinic acid and (4-13C)-nicotinamide were synthesised in an overall and additive yield of 11%. 1H-NMR and mass spectroscopy showed 90% enrichment of 13C in the expected position. NADase-catalysed exchange between thionicotinamide-adenine dinucleotide and (4-13C)nicotinamide furnished (4-13C)NAD+ which was purified, characterized and quantified by 1H-NMR and 13C-NMR spectroscopy and by enzymic assay. The 13C-NMR signal of (4-13C)beta-NAD+ (146.09 ppm) was broadened and shifted (147.83 ppm) upon binding to yeast alcohol dehydrogenase.

1. Samples of (alpha-2H1, 5-2H1) and (alpha-2H1, beta-2H1) urocanic acid were prepared by a combination of chemical and enzymic methods. 2. The enzymic conversion of unlabelled urocanate was followed by 1H-NMR spectroscopy at 500 MHz in deuterium oxide. It was found (a) that urocanase promotes the exchange of the 5-hydrogen atom of the substrate faster than it catalyses the overall reaction, (b) that the product is an equilibrium mixture of racemic beta-(5-oxoimidazol-4-yl)propionate and beta-(5-hydroxyimidazol-4-yl)propionate and (c) that beta-(5-oxoimidazol-4-yl)-propionate is spontaneously hydrolysed under physiological conditions to N-formylisoglutamine. The rate of this hydrolysis is considerably diminished at +8 degrees C. 3. It was shown by ultraviolet and 1H-NMR spectroscopic measurements that beta-(5-hydroxyimidazol-4-yl)-propionate (gamma max approximately equal to 234 nm) exists in protonated from at low pH (less than 1) whereas pH (approximately equal to 7.5) it exists in equilibrium with beta-(5-oxoimidazol-4-yl)propionate (gamma max approximately equal to 269 nm). 4. (alpha-2H1, beta-2H1)Urocanate was reacted with urocanase in deuterium oxide. 1H-NMR spectroscopy at 500 MHz showed a slight incorporation of protium into the side-chain of the product. The incorporated protium corresponded roughly to the protium contamination of the solvent and was equally distributed between the alpha and beta positions. No transfer of the 5-hydrogen atom to the side-chain was detected. 5. Kinetic deuterium isotope effects of between 2 and 3 were measured when the urocanase reaction was conducted in deuterium oxide at different p2H values. 6. Implications of these findings for the mechanism of action of urocanase are discussed.

A preparation containing 80.0 +/- 0.5% (2RS)-methylmalonyl-carba-(dethia)-CoA and 20.0 +/- 0.5% propionyl-carba-(dethia)-CoA was reacted in buffered deuterium oxide with catalytic amounts of coenzyme B12, methylmalonyl-CoA mutase and methylmalonyl-CoA epimerase. The rearrangement of the methylmalonyl-carba-(dethia)-CoA to succinyl-carba-(dethia)-CoA was monitored by recording 500-MHz 1H-NMR spectra in short time intervals. After reaching equilibrium (approximately equal to 28 min) the products showed chemical stability for about 17 h, i.e. succinyl species did not undergo the spontaneous hydrolysis encountered with normal succinyl-CoA. In the pre-equilibrium stage only about 66% of the produced succinyl-CH2CoA was the expected monodeuterated species. The remainder was 15.5% unlabelled and 18.3% 3,3-dideuterated. After reaching equilibrium a continuous deuterium incorporation (washing-in) from the solvent to the products was observed and quantified. The time course of the appearance of unlabelled, mono-, di- and trideuterated succinyl-CH2CoA species was determined by assigning and integrating the isotope-shifted 1H signals from the various species. Furthermore, mutase catalyses slow deuterium incorporation into first the methylene and then the methyl group of propionyl-CH2CoA. On the basis of these data it was concluded that methylmalonyl-CoA mutase and epimerase are responsible for continuous deuterium incorporation and multiple incorporation occurs when the backward reaction (succinyl-CH2CoA----methylmalonyl-CH2CoA) becomes important. To account for all of the results obtained with dethia and natural substrates we propose a new mutase mechanism whereby the enzyme can retain full stereospecificity at C-3 of succinyl while an internal 1,2-H shift to give a C-2 succinyl radical is responsible for partial scrambling of diastereotopic protons at C-3. This mechanism successfully predicts the observed deuterium disproportionation in succinyl species and the order of appearance of di- and trideuterated products via the washing-in process.