Dehydroquinate synthase from Escherichia coli, and its substrate 3-deoxy-D-arabino-heptulosonic acid 7-phosphate.
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Chromatography↗
Biomedical subjects
S Mehdi
Publications and source records attributed to S Mehdi.
Syntheses and configurational analyses of thymidine 4-nitrophenyl [17O,18O]phosphates and the stereochemical course of a reaction catalyzed by bovine pancreatic deoxyribonuclease I.
The syntheses of both diastereomers of thymidine 3'-(4-nitrophenyl [17O,18O]phosphate) [( 17O,18O]TpNP) and of thymidine 5'-(4-nitrophenyl [17O,18O]phosphate) [( 17O,18O]NPpT) and the Rp diastereomer of thymidine 3'-(4-nitrophenyl [17O,18O]phosphate) 5'-(4-nitrophenyl phosphate) [( 17O,18O]NPpTpNP) are described. The absolute configurations of the chiral phosphorus atoms have been determined unambiguously by 31P and 17O NMR spectroscopy. The Rp diastereomer of [17O,18O]NPpTpNP was hydrolyzed in the presence of bovine pancreatic deoxyribonuclease I to yield the Rp diastereomer of thymidine 3'-[16O,17O,18O]-phosphate 5'-(4-nitrophenyl phosphate), demonstrating that the enzyme-catalyzed reaction occurs by a mechanism in which a single displacement reaction occurs at the chiral phosphorus atom.
Animals↗
Oxygen chiral phosphate esters.
During the past four years, methods have been reported for the syntheses and configurational analyses of virtually any phosphate mono- and diester chiral by virtue of oxygen isotope substitution, and these techniques have already been applied to an impressive number of enzymic and chemical reactions. At present, no experimental information is available that contradicts the simplest interpretations that have been applied to the results obtained for enzymic reactions: inversion of configuration indicating a direct displacement of the leaving group by the attacking group, and retention of configuration implying the formation of a phosphorylated or nucleotidylated enzyme intermediate. However, it does seem necessary to further investigate the mechanisms of at least some of the reactions discussed in this review to ensure that the simplest interpretation is correct. For example, the caveat we have raised about the interpretation of inversions of configurations in phosphohydrolase reactions is chemically reasonable, and these reactions should be reexamined to evaluate the importance of covalent catalysis by carboxylate groups. However, for the vast majority of the enzymic reactions that have been investigated, the stereochemical approach to ascertaining whether catalysis involves the formation of covalent intermediates remains the simplest and most direct method.
Binding Sites↗
Stereochemical course of the hydrolysis of thymidine 5'-(4-nitrophenyl [17O,18O]phosphate) in H216O catalyzed by the phosphodiesterase from snake venom.
The phosphodiesterase from snake venom catalyzes the hydrolysis of the Rp diastereomer of thymidine 5'-(4-nitrophenyl [17O,18O]phosphate) in H216O with retention of configuration at phosphorus. This result is in agreement with those previously reported for the hydrolysis of chiral phosphorothioate substrates (Bryant, F. R., and Benkovic, S. J. (1979) Biochemistry 18, 2825-2828; Burgers, P. M. J., Eckstein, F., and Hunneman, D. H. (1979) J. Biol. Chem. 254, 7476-7478). The hydrolysis reaction catalyzed by this enzyme occurs via formation of a covalent nucleotidylated enzyme intermediate.
Animals↗