A β-cyanoalanine (β-(-CNAla)-forming enzyme, which catalyzed the formation of β-CNAla from O-acetyl-L-serine and sodium cyanide, was isolated in crystalline form from Enterobacter sp. 10-1, a cyanide-resistant strain. The purification procedure involved protamine treatment, ammonium sulfate fractionation, column chromatography on DEAE-cellulose, DEAE-Sephadex A50, Sephadex G-100 and hydroxyapatite, and crystallization with ammonium sulfate. The crystalline enzyme was homogeneous by criteria of the ultracentrifugation and polyacrylamide gel electrophoresis.
The enzyme was determined to have a molecular weight of about 68, 000, and consisted of two apparently identical subunits, each having a molecular weight of about 34, 000. The enzyme also catalyzed the formation of cysteine from O-acetyl-L-serine and sodium sulfide, and the cysteine-forming activity was 245 times greater than that of the β-CNAla-forming activity.

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