Changes in orthophosphate, pyrophosphate and long-chain polyphosphate levels in Leishmania major promastigotes incubated with and without glucose.
The intracellular levels of orthophosphate (Pi), pyrophosphate (PPi) and short- and long-chain polyphosphate (Poly P) were measured in Leishmania major promastigotes incubated in a phosphate-free medium. In the absence of exogenous substrate, the levels of both Pi and PPi increased during a 1 h incubation. The increase in both Pi and PPi was prevented when glucose was present, but glycerol prevented the rise in Pi only. A rise in Pi and PPi was also seen in cells incubated in the absence of exogenous substrate under anaerobic conditions. This was reversed upon addition of glucose plus oxygen. Polyphosphate, here shown to be present in L. major, was measured by means of a polyphosphate glucokinase assay. Short-chain Poly P content did not differ between cells incubated for 1 h in the absence of exogenous substrate or in the presence of glucose or glycerol. Long-chain Poly P content, however, was lower in cells incubated without glucose than in cells incubated with glucose and was also lower in cells incubated for 1 h with glycerol as compared with freshly washed cells. Up to 61% of the increase in Pi and PPi that occurred in promastigotes incubated in the absence of exogenous substrate could have arisen from the concomitant decrease in long-chain Poly P.