The L-cysteine desulfhydrase of Escherichia coli.

The coenzyme function of pyridoxal-phosphate in cysteine desulfhydration and in the mechanistically similar serine and threonine dehydration (deamination) processes has been a subject of discussion in a number of recent publications (see, for example, Snell, 1952, and Braunstein and Shemyakin, 1953). A chemical model reaction has been proposed (Metzler and Snell, 1952). Evidence for pyridoxal-phosphate as a cofactor for the L-cysteine desulfhydrase of Proteus morganii is contained in the report by Kallio (1951). Cell-free extracts from Escherichia coli strain E26 and an aureomycin-resistant strain derived from it, however, were not stimulated by the inclusion of pyridoxal-phosphate during the desulfhydration of both the Dand the L-isomers (Saz and Brownell, 1954). The present communication describes the isolation and characterization of an L-cysteine desulfhydrase from a strain of E. coli. Virtually complete resolution for pyridoxal-phosphate has been attained.