MECHANISM OF TRANSMEMBRANE GLUCOSE TRANSPORT IN YEAST - EVIDENCE FOR PHOSPHORYLATION ASSOCIATED WITH TRANSPORT

Glucose transport in Saccharomyces cerevisiae was studied, utilizing iodoacetatepoisoned cells to block fermentation. An initial, rapid, active uptake of about 5 μmoles of glucose per gram yeast could be observed under these conditions. The actively transported glucose could not be recovered from the cells as free glucose. It was found that the transported sugar had been phosphorylated. The intracellular ATP concentration appeared to be far too low to account for this sugar phosphorylation via the hexokinase reaction. ATP synthesis during the experiments could be excluded with a high degree of probability. It appeared that an intracellular conversion of the transported, phosphorylated sugar takes place in iodoacetate-poisoned yeast. The product (or products) of this conversion could not yet be identified. Unlike sugar phosphates, the unknown compound is released again into the medium. Under certain experimental conditions glucose taken up from the medium was phosphorylated by commercial bakers' yeast, whereas free glucose, present inside the cells (liberated from storage carbohydrates) was not phosphorylated. It is shown that the most obvious interpretation of these phenomena is a phosphorylation of glucose associated with transport, with polyphosphates as phosphate donor. This interpretation tallies with a hypothesis on glucose transport, postulated in previous papers. These experimental results are compared with data on sugar transport in various cells, published in recent literature. © 1969.