The effect of 5-thioglucose on the energy metabolism of Schistosoma mansoni in vitro

5-Thioglucose (5-TG) had a marked effect on the energy metabolism of Schistosoma mansoni in vitro: the conversion of external glucose into lactate by intact worms was severely inhibited. This inhibition of glycolysis was instantaneous, independent of the oxygen concentration and competitive with respect to glucose. Degradation of 0.5 mM external (14C-labelled) glucose was inhibited for 80% in the presence of 20 mM 5-TG. On the other hand the degradation of endogeneous glycogen to lactate was uninhibited. This shows that the inhibition of glucose breakdown occurred at the entrance of glucose into the cell and/or at the hexokinase reaction. It was demonstrated that 5-TG inhibited both the uptake of glucose and the activity of hexokinase. However, it was concluded that in the intact worm 5-TG blocked glycolysis by its competitive inhibition of hexokinase. In intact S. mansoni worms hexokinase is probably the rate-limiting enzyme of glycolysis. Krebs-cycle activity and lactate production do not occur at a fixed ratio: at lower rates of pyruvate formation Krebs-cycle activity was favoured.