Désulfhydration et β substitution de la cystéine catalysées par la cystéinelyase du sac vitellin et du jaune de l'oeuf de poule

Abstract

The yolk of incubated hen's eggs contains a pyridoxal phosphate activated enzyme free of iron, copper, magnesium and calcium. This enzyme activates the β-carbon atom of cystein. Its reactivity is demonstrated by the ease with which this β-carbon fixes various sulfur containing substances in which the sulfur has reducing properties: inorganic sulfide, sulfite or cystein itself. In the absence of substances able to react with the β-carbon atom, the active complex, consisting of the enzyme and the aminated tricarbon chain, is hydrolysed to pyruvic acid and ammonia. The liberation of hydrogen sulfide thus appears to be the consequence either of the substitution of the β-carbon atom of cystein or of the decomposition of the comples which this aminoacid forms with the enzymes studies. The latter seems therefore to possess an acitivity which differs from the activity of the desulfhydrases as yet known. We suggests to call this enzyme cysteinelyase.