REACTIVATION OF TRIOSEPHOSPHATE ISOMERASE FROM 3 TRYPANOSOMATIDS AND HUMAN - EFFECT OF SURAMIN

The reactivation of the homodimeric triosephosphate isomerases (TIMs) from Trypanosoma brucei, T. cruzi, Leishmania mexicana and humans was determined after their denaturation with guanidine hydrochloride. In t he range of 2-32 mu g of T. brucei TIM per ml and 0.2-5 mu g of the ot her enzymes per ml, the rate and extent of TIM reactivation depended o n protein concentration, indicating that at these protein concentratio ns, the rate-limiting step of reactivation is monomer association and not monomer folding. The rate of monomer association was more than one order of magnitude lower in the T. brucei enzyme than in the other th ree enzymes. Suramin is a drug of choice in the treatment of sleeping sickness, but its mechanism of action is not known. At micromolar conc entrations, Suramin inhibited the reactivation of the four enzymes, bu t the extent of inhibition by Suramin decreased with increasing protei n concentration as consequence of a diminution of the life time of the folded monomer. Since the life time of the monomer of T. brucei TIM i s longer than that of the other enzymes, Suramin is a more effective i nhibitor of the reactivation of TIM from T. brucei, particularly at mo nomer concentrations above 1 mu g of protein per ml (monomer concentra tion approx. 37 nM). Compounds that are structurally related to Surami n also inhibit TIM reactivation; their effect was about five times mor e pronounced in the enzyme from T. brucei than in human TIM.