Formation of extracellular adenosine triphosphate by normal and neoplastic human cells in culture

Normal and neoplastic human cells in culture were suspended under isotonic conditions and incubated for one minute with the substrates, including ³²P-labelled inorganic phosphate, and cofactors of the glyceraldehyde-3-phosphate dehydrogenase and phosphoglycerate kinase reactions (complete medium), as well as with an incomplete medium lacking ADP, NAD⁺ and glyceraldehyde-3-phosphoric acid. The neoplastic cell types incubated in the complete medium synthesized three to six times more labelled ATP than the corresponding normal cells. In the incomplete medium only insignificant amounts of labelled ATP were formed during one-minute incubation by all types of cells. From other types of experiments it could be concluded that the labelled ATP, isolated from the cells incubated in the complete medium, was formed at the surface of the cell membranes. Only negligible amounts of enzymes engaged in the synthesis of ATP have leaked out from the cells.