Regulation of Hexose Transport in Chlorella vulgaris

Of nine species of unicellular algae tested, Chlorella vulgaris showed the highest inducibility for an active hexose transport system. Whereas the rate of uptake in all other species was increased by induction less than 5-fold, it was increased more than 400-fold in one strain of C. vulgaris. With glucose as inducer, the minimum time necessary to synthesize inducible proteins of the transport system was 15 minutes. The Km for induction with glucose is 5 mum and with 6-deoxyglucose 1 mm. The inducing sugars have to penetrate the cells to be effective.Evidence indicating that regulation of induction occurs at the transcriptional level was obtained. The induction was inhibited by 6-methylpurine. When cells were exposed to induce in the presence of actidione no increase in transport activity could be measured. After removal of actidione as well as the inducer, an increased uptake activity was observed after 30 to 60 minutes. The induced uptake system showed a turnover with a half-life of 4 to 6 hours at 26 C under nongrowing conditions; at 0 C turnover was negligible. Turnover was partly inhibited by anaerobic condition and by actidione; it was accelerated under growing conditions.