PMID:4555420
| Citation |
Lambert, MP and Neuhaus, FC (1972) Mechanism of D-cycloserine action: alanine racemase from Escherichia coli W. J. Bacteriol. 110:978-87 |
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| Abstract |
The antibiotic d-cycloserine is an effective inhibitor of alanine racemase. The lack of inhibition by l-cycloserine of alanine racemase from Staphylococcus aureus led Roze and Strominger to formulate the cycloserine hypothesis. This hypothesis states that d-cycloserine has the conformation required of the substrates on the enzyme surface and that l-cycloserine cannot have this conformation. Alanine racemase from Escherichia coli W has been examined to establish whether these observations are a general feature of all alanine racemases. The enzyme (molecular weight = 95,000) has Michaelis-Menten constants of 4.6 x 10(-4)m and 9.7 x 10(-4)m for d- and l-alanine, respectively. The ratio of V(max) in the d- to l-direction is 2.3. The equilibrium constant calculated from the Haldane relationship is 1.11 +/- 0.15. Both d- and l-cycloserine are competitive inhibitors with constants (K(i)) of 6.5 x 10(-4)m and 2.1 x 10(-3)m, respectively. The ratio of K(m)d-alanine to K(i)d-cycloserine is 0.71, and the ratio of K(m)l-alanine to K(i)l-cycloserine is 0.46. Since l-cycloserine is an effective inhibitor, it is concluded that the cycloserine hypothesis does not apply to the enzyme from E. coli W. |
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| Keywords |
Alanine/metabolism; Ammonium Sulfate; Butanols; Carbon Isotopes; Cell Fractionation; Cell-Free System; Centrifugation, Density Gradient; Chemical Precipitation; Chromatography, Gel; Chromatography, Ion Exchange; Cycloserine/pharmacology; Electrophoresis, Disc; Escherichia coli/enzymology; Escherichia coli/growth & development; Hydrogen-Ion Concentration; Isomerases/antagonists & inhibitors; Isomerases/isolation & purification; Isomerases/metabolism; Molecular Weight; Protamines; Stereoisomerism; Sucrose; Sulfates |
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