A 31P-NMR study of phosphate transport and compartmentation in Candida utilis

The recovery of Candida utilis from phosphate starvation was studied using 31P-NMR. The phosphate analogue methylphosphonate was found to be a useful indicator of cytosol pH. Added orthophosphate was rapidly accumulated by the cells and stored mainly In a stable pool of polyphosphate of mean chain-length at least 200 units. Observed pH changes in the medium and cytosol during uptake of orthophosphate and methylphosphonate are consistent with the transport of these compounds across the plasma membrane by a proton/phosphate symport. However, transport of phosphate across the vacuole membrane occurs by a mechanism for which methylphosphonate is not a substrate. In the cytosol pH changes are strongly correlated with changes in orthophosphate concentration, however, this is not the case in the vacuole.