What question did this study set out to answer?

Determine whether the cycloserine hypothesis, which posits that only d-cycloserine inhibits alanine racemase, applies to the enzyme from Escherichia coli W.

June 1, 1972Journal of BacteriologyOpen Access

Mechanism of d -Cycloserine Action: Alanine Racemase from Escherichia coli W

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Authors

MLMary P. LambertChildren's Hospital of Philadelphia FNFrancis C. NeuhausNorthwestern University

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Implication

Enzyme kinetic analysis reveals competitive inhibition by both cycloserine enantiomers in Escherichia coli, indicating the cycloserine hypothesis is not universally applicable.

Key Points

Determine whether the cycloserine hypothesis, which posits that only d-cycloserine inhibits alanine racemase, applies to the enzyme from Escherichia coli W.
Characterized purified alanine racemase (molecular weight 95,000) from Escherichia coli W by measuring kinetic parameters in both reaction directions.
Calculated inhibition constants (Ki) for d-cycloserine and l-cycloserine to determine the mode of inhibition relative to d- and l-alanine substrate affinities.
Michaelis-Menten constants (Km) were 4.6 x 10^-4 M for d-alanine and 9.7 x 10^-4 M for l-alanine, with a d- to l-direction Vmax ratio of 2.3 and an equilibrium constant of 1.11 +/- 0.15.
Both d- and l-cycloserine functioned as competitive inhibitors with Ki values of 6.5 x 10^-4 M and 2.1 x 10^-3 M, respectively.
The Km to Ki ratio was 0.71 for the d-enantiomers and 0.46 for the l-enantiomers, refuting the cycloserine hypothesis for this specific bacterial enzyme.

Cite This Study

Lambert et al. (1972) studied this question.

synapsesocial.com/papers/6a79e0d2b2ad017e403216a1 https://doi.org/10.1128/jb.110.3.978-987.1972

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Implication

Enzyme kinetic analysis reveals competitive inhibition by both cycloserine enantiomers in Escherichia coli, indicating the cycloserine hypothesis is not universally applicable.

Mechanism of d -Cycloserine Action: Alanine Racemase from Escherichia coli W

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Cite This Study

Mechanism of d -Cycloserine Action: Alanine Racemase from Escherichia coli W

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Implication

Key Points

Cite This Study

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