The Activity of Crystalline Urease as a Function of Oxidation-reduction Potential*

A number of different enzymes are activated by certain reducing agents (e.g., KCN, H&S, cysteine, and reduced glutathione) and inactivated by oxidizing agents (e.g., K3Fe(CN)&, HzOz, and cystine). Under ideal conditions such inactivation is reversible by the addition of reducing agents (for a review of this subject cJ Hellerman (1937, 1939)). These results have been interpreted on the basis of the oxidation or reduction of substituent sulfhydryl groups in the enzyme molecule which are concerned with enzyme activity; it is proposed that the enzyme is active when the sulfur is in the reduced -SH form but inactive when it has the oxidized -S-Sconfiguration. In the case of urease the presence of sulfhydryl groups in the enzyme molecule has been demonstrated (Sumner and Poland, 1933) and it has also been shown that as the enzyme activity disappears there is a corresponding loss in sulfhydryl groups (ci. Hellerman (1939)). Sizer (1939, 1940, 1941) has demonstrated the fact that the activation energy of the urease-urea system may be modified by the presence of oxidizing or reducing agents, suggesting a change in the enzyme surface effected by these compounds. Apparently not all of the sulfhydryl groups are concerned with enzyme activity, however, for when the more readily detectable sulfhydryl groups have been rapidly oxidized with porphyrindin the urease activity is unchanged (Hellerman, 1939). With papain as well it is apparently the less reactive sulfhydryl groups which are concerned with enzyme activity (Hellerman, 1939). In the case of papain, which