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B6db references: 85226342

type Journal Article
authors Rosenberg, R. M.; O'Leary, M. H.
title Aspartate beta-decarboxylase from Alcaligenes faecalis: carbon-13 kinetic isotope effect and deuterium exchange experiments
journal Biochemistry
ui 85226342
year (1985)
volume 24
number 7
pages 1598-603.
keywords Alcaligenes/*enzymology
abstract We have measured the 13C kinetic isotope effect at pH 4.0, 5.0, 6.0, and 6.5 and in D2O at pD 5.0 and the rate of D-H exchange of the alpha and beta protons of aspartic acid in D2O at pD 5.0 for the reaction catalyzed by the enzyme aspartate beta-decarboxylase from Alcaligenes faecalis. The 13C kinetic isotope effect, with a value of 1.0099 +/- 0.0002 at pH 5.0, is less than the intrinsic isotope effect for the decarboxylation step, indicating that the decarboxylation step is not entirely rate limiting. We have been able to estimate probable values of the relative free energies of the transition states of the enzymatic reaction up to and including the decarboxylation step from the 13C kinetic isotope effect and the rate of D-H exchange of alpha-H. The pH dependence of the kinetic isotope effect reflects the pKa of the pyridine nitrogen of the coenzyme pyridoxal 5'-phosphate but not that of the imine nitrogen. A mechanism is proposed for the exchange of aspartate beta-H that is consistent with the stereochemistry suggested earlier.
last changed 2002/11/12 16:17

B6db references