The inhibition of succinoxidase by heavy metals and its reactivation with dithiols

Abstract

A large number of heavy metals inhibited the enzyme activity of succinoxidase. The inhibition was due to combination of the metal with the -SH groups of the protein moiety. Bt, Cd, and HgCl2 had the greatest inhibitory power, producing 90% inhibition at about 10-5 M cone. V, Zn, and Pb produced effective inhibitions at about 10-4 M. Zn and Sb required higher concs., half-inhibition being attained at about 1.5 X 10-3 M. The inhibition produced by these heavy metals was reversed on addition of dithiols. The most effective compounds for the reversal of Bi, Hg, and Cd inhibition were l:3-propanedithiol, l:3-dimercaptopro-panol and 2:3 -dimercaptopropionic acid. 1:3 -Propanedithiol was the only effective agent for the reversal of V inhibition. 1:3-Dimercaptopropanol and l:3-propanedithiol were effective against Se inhibition. Reversal by BAL (2:3-di-mercaptopropanol) occurred only at higher cones. Gluta-thione at the cones, used with dithiols was generally ineffective; at higher cones, it produced reactivation. Reversal of inhibition became increasingly difficult when the conc, of inhibitor was raised so as to produce complete inhibition.