A confirmation of the proposed model for the hexose uptake system ofChlorella vulgaris. Anaerobic studies in the light and in the dark

Summary

Energy for accumulation of sugar analogues inChlorella vulgaris can be supplied by respiration and by light. Under anaerobic conditions a quantum efficiency of close to one has been determined for light-dependent uptake of 6-deoxyglucose at 712 nm. Although the rate of uptake under anaerobic conditions in the dark is less than 15% of that in the light, the steady-state plateau of accumulation does not change when the light is turned off. This is explained by the observation that efflux of sugar is inhibited by lack of energy to the same extent as influx. This agrees with a model proposed earlier (Komor, Haass & Tanner,Biochim. Biophys. Acta 266:649, 1972). Under aerobic conditions during the steady-state plateau in the dark, the rate of influx of 6-deoxyglucose is twice that of initial influx (positive transmembrance effect). By anaerobiosis the initial influx is almost completely inhibited, whereas the steady-state influx is affected only to 50%. This points to an energyless “homoexchange.” However, this flux is completely inhibited by uncoupling agents. To explain these results, the existence of an energygenerating efflux has been assumed, which is affected by uncouplers. The efficiency of energy production by efflux and the re-use of this energy for influx is inversely related to the amount of energy supplied by other energy-generating processes in the cells; under anaerobic conditions in the dark, 90% of the efflux energy seems to be available for influx.