Purification and characterization of cystathionine γ‐synthase type II from Bacillus sphaericus

Cystathionine γ‐synthase type II, which catalyzes l‐cystathionine synthesis from O‐acetyl‐l‐homoserine and l‐cysteine was purified from Bacillus sphaericus (IFO 3536) in seven steps. The purified enzyme appeared to be homogeneous by the results of polyacrylamide electrophoresis and ampholyte electrofocusing. The enzyme is a typical pyridoxal‐P dependent enzyme, has a molecular mass of 165 kDa and consists of four subunits identical in molecular mass. The enzyme catalyzed the γ‐replacement reaction and the elimination reaction was hardly detected even when a large amount of enzyme was added. In the replacement reaction, O‐acetyl‐l‐homoserine and the following thiol compounds: L and d‐cysteine, L and d‐homocysteine, sodium sulfide, various alkyl and aryl mercaptans, acted as the most suitable substrate to produce l‐cystathionine and the corresponding S‐substituted l‐homocysteine derivatives.