Mechanism of Inactivation of α-Amino-ε-caprolactam Racemase by α-Amino-δ -valerolactam

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Both D- and L-α-amino-δ-valerolactam inactivated α-amino-ε-caprolactam racemase during incubation with the enzyme. The degree of inactivation increased with increases in pH and the concentration of L-α-amino-δ-valerolactam in the incubation mixture. Pyridoxal 5-phosphate reactivated the inactivated enzyme, and glyoxylate and other α-keto acids such as pyruvate, phenylpyruvate, and α-ketobutyrate protected the enzyme from inactivation by L-α-amino-δ-valerolactam. Both the enantiomers of methionine were produced when α-keto-γ-methylthiobutyrate was incubated with the enzyme in the presence of L-α-amino-δ-valerolactam. Thus, the inactivation of the enzyme in terms of a-amino-ocaprolactam racemization activity is due to conversion of the enzyme-bound pyridoxal 5-phosphate into pyridoxamine 5-phosphate by a transamination with L-α-amino-δ-valerolactam. Formation of pyridoxamine 5-phosphate from the enzyme-bound pyridoxal 5-phosphate was proved by spectrophotometry and thin layer chromatography. The rate of racemization of L-α-amino-δ-valerolactam was calculated to be 48 times faster than that of the transamination with glyoxylate.
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