Bacteria desulfhydrases

Hydrogen sulfide is a well known general metabolite produced on sulfate reduction by certain bacteria. Moreover, organic forms of sulfur can give rise to HS , hence H2S in certain bacteria. Thus, cysteine desulfhydrase (EC 4.4.1.1, cystathionine y-lyase) converts L-cysteine to H2S, pyruvate, and NH3. This enzyme shows a requirement for pyridoxal phosphate and the unstable ami-noacrylic acid is an intermediate (Equation 1) in the reaction ... 

Enzymes that possess the same catalytic activity but are evolutionarily unrelated and play very diverse biological functions can be found, for example, in a group of PLP-dependent enzymes with desulfhydrase activity, that is, enzymes that release H2S from thiol amino acids. Bacteria employ desulfhydrases not only in the metabolism of sulfurated amino acids and in the adaptation to new nutrient sources, but also, sometimes, as virulence factors. An E. coli enzyme with desulfhydrase activity is even known to act as a modulator of gene expression, although this function seems to be unrelated to catalysis. Sulfide production by PLP-dependent enzymes is also important in vertebrates, where H2S has been shown to act as a neuromodulator. " ... 

Support for this enzymic desulfhydration came from the work of Metzler and Snell (72), who proposed a detailed chemical mechanism of desulfhydration in model experiments in the presence of pyridoxine and a metal ion. Similar enzyme models were proposed by others (73). The enzymic aspect of this reaction is not entirely satisfactory however, ce relatively little is known of the desulfhydrase enzyme, either derived from the liver (74) or from bacteria (75). In addition several pyridoxal phosphate-protein enzymes can catalyze cysteine desulfhydration (see Section IV). 

Cysteine can be determined by a bacteria of the type Proteus morganii. The enzyme involved, cysteine desulfhydrase, catalyses the reaction ... 

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