Phosphorus-31 and carbon-13 nuclear magnetic resonance studies of glucose and xylose metabolism in Candida tropicalis cell suspensions

Abstract

The metabolism of glucose and xylose was studied as a function of oxygenation in suspensions of Candida tropicalis by 31P and 13C nuclear magnetic resonance spectroscopy. Both the rate of carbohydrate metabolism and the cytoplasmic pH were independent of the rate of oxygenation in cells metabolizing glucose. However, these two parameters were markedly dependent on the rate of oxygenation in C. tropicalis cells metabolizing xylose. For example, the cytoplasmic pH in fully oxygenated xylose-metabolizing cells was 7.8 but decreased to 6.3 in anoxic cells. In general, suspensions of cells consuming xylose had a lower rate of sugar uptake, a more acidic cytoplasmic pH, lower levels of sugarphosphomonoesters (SP) and ATP, higher levels of intracellular Pi, a more alkaline vacuolar pH, and a lower rate of extracellular Pi assimilation and polyphosphate synthesis than cells consuming glucose. These observations indicate that C. tropicalis metabolizing xylose is less energized than glucose-metabolizing cells. On both carbon sources, however, an inverse correlation between intracellular levels of SP and Pi was observed. Also, uptake of extracellular Pi correlated with the synthesis of polyphosphates within the cells. During anoxia, Pi was not taken up, and polyphosphates were hydrolyzed instead to fulfill the cells' requirements for phosphate.