The effect of calcium ions on the glycolytic activity of Ehrlich ascites-tumour cells.

1. Added Ca(2+) inhibited lactate formation from sugar phosphates by intact Ehrlich ascites-tumour cells. Lactate formation from glucose by these cells was unaffected by added Ca(2+). 2. The Ca(2+) inhibition of lactate formation by intact cells occurred in the extracellular medium. 3. Intact ascites-tumour cells did not take up Ca(2+)in vitro. 4. Glycolysis of sugar phosphates by cell extracts as well as pyruvate formation from 3-phosphoglycerate and phosphoenolpyruvate was inhibited by Ca(2+). 5. It was concluded that Ca(2+) inhibited the pyruvate-kinase (EC 2.7.1.40) reaction. Further, Ca(2+) inhibition of pyruvate kinase could be correlated with the overall inhibition of glycolysis. 6. Concentrations of Ca(2+) usually present in Krebs-Ringer buffers, inhibited glycolysis and pyruvate-kinase activity by approx. 50%. 7. The inhibition of glycolysis by added Ca(2+) could be partially reversed by K(+) and completely reversed by Mg(2+) or by stoicheiometric amounts of EDTA. 8. The hypothesis is advanced that the inability of tumour cells to take up Ca(2+) is a factor contributing towards their high rate of glycolysis.