RESPIRATORY INHIBITORS AFFECT INCORPORATION OF GLUCOSE INTO SACCHAROMYCES-CEREVISIAE CELLS, BUT NOT THE ACTIVITY OF GLUCOSE-TRANSPORT

Incubation of starved galactose-grown S. cerevisiae cells with cyanide reduced glucose uptake as measured over a 5-s period. The V-max for g lucose uptake was decreased by over a factor of two but the apparent a ffinity for glucose doubled. When measured in the sub-second time scal e, however, there was-no significant inhibition of glucose uptake, by cyanide, up to 200-ms, clearly demonstrating that, in cyanide treated cells, glucose uptake was not linear for the first 5-s. After a 200-ms exposure of untreated cells to radio-labelled glucose, less than 10% of the intracellular label resided in soluble uncharged compounds. In cyanide-treated cells up to 43% of the labelled compounds were uncharg ed, with a concurrent reduction of intracellular label residing in ani onic compounds. The results suggest that, in the presence of 10 mM cya nide when respiration is inhibited, a reduction in the cellular ATP co ncentration causes a reduction in hexose-kinase activity which results in an accumulation of internal free glucose, which in turn causes a r eduction in net glucose transport.