Rashid B, Manzoor N, Khan LA

Language: English
References: 16
Page: 55-59
PDF size: 108.45 Kb.

ABSTRACT

Rate of H⁺ efflux and its stimulation by nutrients/analogs have been quantified in cells and spheroplasts of Candida albicans. In the absence of any nutrient, yeast cells showed an average H⁺ efflux rate of 22.3 nmoles/min/mg yeast cells. Addition of 5mM Glucose to the medium resulted in striking stimulation of H⁺ efflux by 7.5 fold. Supplementation of medium with 2-deoxy-D-glucose, Arginine & Glutamic acid lead to a minimal stimulation of 1.37, 1.50 & 1.42 fold, respectively, over control. Xylose, Lysine and Proline were non-effective. Control Spheroplasts had an H⁺ efflux rate of 2.0 nmoles/min/mg yeast cells. Glucose stimulation of H⁺ efflux was markedly reduced (2.22 fold). H⁺ efflux did not significantly differ from control following supplementation of spheroplasts with either analogs of glucose (2-deoxy-D-glucose, xylose) or amino acids (Arginine, Lysine, Proline, Glutamate). These results have been compared with effect of nutrient/analogs on ATP hydrolytic cycle of isolated PM-ATPase reported earlier by this lab. Percentage of enzyme population going over to E.ADP.P complex stage following mixing with glucose and glutamate (94% & 96%, respectively) is comparable to Control (100%). Mixing of PM-ATPase with ATP in the presence of other nutrients/analogs leads to very significant reduction in population of E.ADP.P. Proportion of E.ADP.P complex which completes formation and dissociation of E~P complex (Power-Stroke) is similar to control in the presence of all nutrients/analogs except for glucose. Population of PM-ATPase molecule completing full ATP hydrolytic cycle is highest in presence of glucose (86.4%). This figure is only 27% for control, 27.8% for glutamate, and is significantly less in presence of other nutrients/analogs (ranging from 4.2% for Lysine to 20.5% for Xylose). Glucose positively affects both legs of hydrolytic cycle, while other nutrients/analogs negatively effect first leg of cycle and are neutral with respect to second leg. Exceptional Glucose stimulation of H⁺ efflux by Candida cells can therefore be correlated with the stimulation of second leg of the ATP hydrolytic cycle.

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