Phosphorus Turnover in Yeast

When bakers yeast cells (Sacckaromyces cerevisiae) were suspended for 1.5 hours at 22°C. in (o) glucose-salt, (6) fluoride-glucose-salt, or (c) sustaining salt media, to each of which radiophosphorus in form of phosphate had been added, Lawrence et al. (112) found radioactivity only in those cells suspended in the first solution. The uptake of radiophosphorus varied with the concentration of glucose. 

By use of ice-cold 5% trichloroacetic acid and hot ether-alcohol solutions, it was determined that approximately 80% of the activity was found in the acid-soluble and 20% in the nucleoprotein fractions. (Approximately 40% of the activity of the nucleoprotein fraction was present in the nucleic acids.) lodoacetic acid decreased while cyanide increased the rate of uptake of radiophosphorus in the nucleoprotein fraction. Once the yeast cells had incorporated P, it was not lost by resuspending the cells in a radiophosphorus-free medium. Hevesy et al. 

It was furthermore found by Malm (120) that the uptake of P by cells depends on pH of the solution in which the cells are suspended. A maximum uptake takes place with pH reaches values of 4-5, while at pH 7 practically no uptake of P is observed. As pH of the cells is not influenced by changes in pH of the nutritive solution, this observation suggests that processes going on at the cell surfaces or within the cell boundary play an important part in phosphorus metabolism in yeaft. 

Lindahl and associates (115a) found recently that radioactive phosphate introduced into the cells of bakers yeast was incorporated into the coenzyme molecule. The rate of this process was under certain conditions dependent on the rate of metabolism but the phosphate exchange also took place in the absence of exogenous substrate at low temperature (-1-4°C.), though at a very slow rate. 

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