P-31 AND C-13 NUCLEAR-MAGNETIC-RESONANCE STUDIES OF GLUCOSE AND XYLOSE METABOLISM IN CANDIDA-TROPICALIS CELL-SUSPENSIONS

The metabolism of glucose and xylose was studied as a function of oxyg enation in suspensions of Candida tropicalis by P-31 and C-13 nuclear magnetic resonance spectroscopy, Both the rate of carbohydrate metabol ism and the cytoplasmic pH were independent of the rate of oxygenation in cells metabolizing glucose. However, these two parameters were mar kedly dependent on the rate of oxygenation in C, tropicalis cells meta bolizing xylose, For example, the cytoplasmic pH in fully oxygenated x ylose-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 sugarphos phomonoesters (SP) and ATP, higher levels of intracellular P-i, a more alkaline vacuolar pH, and a lower rate of extracellular P-i assimilat ion and polyphosphate synthesis than cells consuming glucose. These ob servations indicate that C, tropicalis metabolizing xylose is less ene rgized than glucose-metabolizing cells. On both carbon sources, howeve r, an inverse correlation between intracellular levels of SP and P-i w as observed, Also, uptake of extracellular P-i correlated with the syn thesis of polyphosphates within the cells. During anoxia, P-i was not taken up, and polyphosphates were hydrolyzed instead to fulfill the ce lls' requirements for phosphate.