Sulfhydryl Compounds and Crystalline Urease

Perlzweig 1 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-enzyme for urease is present in the soy bean, or the jack bean. 2 However, in view of the statements of Perlzweig we have undertaken experiments to ascertain the connection between crystalline urease and the sulfhydryl groups.

Perlzweig refers to studies of Waldschmidt-Leitz and his students upon the significance of sulfhydryl compounds in enzymatic reactions. 3 Attention should be called to the fact that the claim made by Waldschmidt-Leitz that liver arginase is wholly inactive in the absence of sulfhydryl compounds, while it is active in the presence of hydrogen sulfide, cysteine, or reduced glutathione has been vigorously denied by Edlbacher, Kraus, and Walter, 4 as well as by Klein and Ziese, 5 who claim that arginase is never activated by cysteine or by glutathione, but instead is inhibited.