Über den mechanismus der katalase-wasserstoffperoxid-reaktion I. Der disulfid- und sulfhydrylgehalt der rinderleber-katalase

• 1.

  1. The amperometrically titratable disulfide and sulfhydryl content of beef-liver catalase is not constant. It changes with enzyme activity, pH and after the action of weak oxidizing agents. As a rule, the ratio disulfide: sulfhydryl increases with increasing enzyme activity. With variation of pH latent sulfhydryl groups are released, and free sulfhydryl groups are masked. The pK of this equilibrium reaction is 7.18. Through the action of oxidizing agents, some sulfhydryl groups can be oxidized to disulfide groups.

• 2.

  2. When the sulfhydryl groups of catalase are blocked by Hg²⁺ or C₆H₅Hg⁺ a loss of enzyme activity occurs. The loss of activity with increasing Hg²⁺ or C₆H₅Hg⁺ concentration may be represented as an equilibrium curve. The change of activity on blocking the prosthetic groups with azide can be expressed in the same way.

• 3.

  3. The dissociation of the proton from the sulfhydryl group was followed by electrometric titration. The dissociation constant was found to be 2.00 · 10⁻⁹ M (at 0°).