On the availability of certain metabolites at the outer surface of normal and malignant cells for the membranous de novo synthesis of ATP and other nucleotides.

The formation of ATP at the cell surface of intact glia and glioma cells in culture has been established. The ATP-forming capacity at the surface of the malignant cells was several times greater than that of the normal glia cells. The ATP-forming capacity was about the same on reincubation one hour after the first incubation. The cells were kept in Eagle's medium in the meantime. ADP, NAD+ and 3-phosphoglyceraldehyde could all be available from a postulated intramembranous metabolic pool and take part in biochemical reactions at the cell surface, provided that albumin was not present in the incubation medium. An incubation medium which was complete except for 3-phosphoglyceraldehyde was only slightly less effective as regards ATP formation at the surface of both glia and glioma cells, compared with the complete incubation medium. The presence of nucleoside diphosphate kinase at the glioma cell surface was confirmed. When intact cells were incubated with only the phosphoryl group donor (ATP) of the reaction but with the acceptor nucleoside diphosphates (CDP, GDP, UDP) ommitted, only CTP and GTP were formed. No UTP was found. Thes latter results indicate that both CDP and GDP are available from the postulated intramembranous metabolic pool, while UDP is not.