Properties of α-Amino-ε-caprolactam Racemasefrom Achromobacter obae

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α-Amino-ε-caprolactam racemase, which occurs in the cytoplasmic fraction of Achromobacter obae, has been purified to homogeneity. It has a monomericstructure with a molecular weight of approximately 50, 000. The absorption spectrum of the enzymeexhibits maximaat 280 and 412 nm at pH 7.3, and is independent of pH from 6.0 to 8.0. One mole ofpyridoxal 5-phosphate is bound per mol of the enzyme.Incubation of the enzymewith hydroxylamineresulted in the formation of the apoenzyme.d- and L-a-Amino-a-caprolactamsare the only substrates. Themaximumactivity is found at pH 8.8 for both the isomers. Michaelis constants are as follows: 8him for D-α-amino-ε-caprolactam, 6 mMfor L-α-amino-e-caprolactam and 2.1×10-7 M for pyridoxal 5-phosphate. The enzyme is inhibited significantly by CuSO4, HgCl2, thiol reagents such as N-ethylmaleimide and p-chloromercuribenzoate, and carbonyl reagents (e.g., phenylhydrazine and hydroxylamine). a- Amino-e-caprolactam racemase catalyzes the α-proton exchange of the substrate with deuteron during racemization in deuterium oxide.
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