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.