Perlzweig1 states that both crystalline urease and extracts of jack bean meal give a positive sulfhydryl test with nitroprusside and that the more active preparations give stronger tests than the weaker ones. He estimates one of his samples of jack bean meal to contain the equivalent of 70 mg. of glutathione per 100 gm. and believes the substance in the meal to be glutathione, rather than cysteine, since the material is negative to the Sullivan reaction until after hydrolysis. He suggests that urease activity is due in part to the sulfhydryl compound and that it may be possible to separate a sulfhydryl activator from the urease proper.We have independently observed that urease, prepared from jack bean meal by the Sumner procedure and twice recrystallized from 30% alcohol, produces a moderate amount of red color when treated with nitroprusside, ammonium sulfate and ammonia, and had ascribed this reaction to the presence of sulfhydryl groups attached to the urease molecule. It was recently shown that no co-...