The stoicheiometry of the absorption of protons with phosphate and L-glutamate by yeasts of the genus Saccharomyces

Abstract

1. A study was made of the pH changes occurring when 0.1-4 mumol of glutamate, phosphate and certain phosphate esters was added at about pH 4.8 to washed cell preparations (50 mg dry wt.) of strains of Saccharomyces. The system also contained deoxyglucose and antimycin to inhibit energy metabolism and so prevent proton ejection from the yeast. 2. A strain of Sacc. carlsbergensis was grown in a chemostat with a limiting supply of phosphate in order to enhance the subsequent rate of phosphate transfer into the yeast. These preparations absorbed 0.2 mumol of phosphate with about 3 equiv. of protons/mol of phosphate. The charge balance was maintained by the efflux of 2 equiv. of K-+ from the yeast. 3. Larger amounts of phosphate were absorbed with fewer proton equivalents. 4. Arsenate and phosphate caused similar pH changes. 5. Glucose 6-phosphate, ATP and certain order phosphate esters each initiated a rise in pH, possibly because hydrolytic extracellular enzymes released phosphate that was subsequently absorbed. 6. Four strains of yeast were grown with glutamate as principal source of nitrogen. Each absorbed extra protons in the presence of L-glutamate. 7. One of them, a strain of Sacc. cerevisiae, absorbed 0.2 mumol of glutamate with 3equiv. of protons/mol of glutamate, and in these circumstances 1-2 equiv. of K-+ left the yeast cells. 8. The role of ionic gradients in the transport of these anions is discussed.