ABSTRACT
The in vitro inhibition of several rat testis dehydrogenases by gossypol was examined. Inclusion of the coenzyme (substrate for NADP+-isocitrate dehydrogenase) in the preincubation mixture containing the enzyme and gossypol, protected the enzymes against inhibition by gossypol. Lactic dehydrogenase-X was amongst the least protected enzymes. This, coupled with its low Ki for gossypol makes it one of the most vulnerable target enzymes in vivo for gossypol action. The inhibition kinetics for lactic dehydrogenase-X were competitive when NADH was present during preincubation, but non-competitive when the coenzyme was excluded during preincubation. In the latter condition, the enzyme seems to undergo progressive inactivation with time causing a nonreversible type of inhibition.