Cystathionine γ-lyase of Streptomyces phaeochromogenes. The occurrence of cystathionine γ-lyase in filamentous bacteria and its purification and characterization

Cystathionine γ-lyase (EC 4.4.1.1) is widely distributed in actinomycetes, e.g. genera Streptomyces, Micromonospora, Micropolyspora, Mycobacterium, Nocardia, Streptosporangium, and Streptoverticillium. The enzyme was purified from Streptomyces phaeochromogenes (IFO 3105) in nine steps. After the last steps, the enzyme appeared to be homogenous by the criteria of polyacrylamide gel electrophoresis, analytical centrifugation, and double diffusion in agarose. The enzyme crystallized in the apo form with the addition of ammonium sulfate. The enzyme has a molecular weight of about 166,000 and consists of four subunits identical in molecular weight. The enzyme exhibits absorption maxima at 278 and 421 nm and contains 4 mol of pyridoxal 5'-phosphate/mol of enzyme. L-Cystathionine, L-homoserine, DL-lanthionine, L-djenkolic acid, and L-cysteine are cleaved as preferred substrates by the Streptomyces enzyme. The α,β-elimination reaction of L-cystathionine is also catalyzed by the enzyme at a ratio of about one-seventh of the α,γ-elimination reaction. Cystathionine β-synthase (EC 4.2.1.22) and cystathionine γ-synthase (EC 4.2.99.9) activities were also detected in crude extracts of S. phaeochromogenes, but cystathionine β-lyase (EC 4.4.1.8) was not. Consequently, the reverse transsulfuration pathway in actinomycetes may be similar to that in yeast and molds.