Xg. Gao et al., REACTIVATION OF TRIOSEPHOSPHATE ISOMERASE FROM 3 TRYPANOSOMATIDS AND HUMAN - EFFECT OF SURAMIN, Biochemical journal, 332, 1998, pp. 91-96
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.