6225 step.20 The present findings strengthen the possibility of a direct role for sulfur in catalysis by adenosine deaminase. Deficiencies of the sulfur nucleophiles, which could be satisfied by the intervention of other catalytic groups, are their relatively slow rates of reaction compared with enzymes and the direction of cleavage of the glutathione derivative in alkali. This latter re(20) R. Wolfenden, T. I
