Membrane-bound ATP fuels the Na/K pump. Studies on membrane-bound glycolytic enzymes on inside-out vesicles from human red cell membranes.

Open Access
Publisher Website
Google Scholar
Abstract
ATP stimulates Na transport into inside-out vesicles (IOV) made from human red cell membranes; strophanthidin inhibits the ATP-stimulated transport. The substrates for glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and phosphoglycerate kinase (PGK) (glycolytic enzymes bound to the cytoplasmic surface of the red cell membrane) also stimulate Na transport into IOV without added ATP. The elution of GAPDH from the membranes prevents the stimulation by the substrates, but not by exogenous ATP. Hexokinase plus glucose (agents that promote breakdown of ATP) prevent stimulation of Na transport by exogenous ATP but not by the substrates for GAPDH and PGK. [32P]Pi is incorporated into a membrane-bound organic phosphate compound shown chromatographically to be ATP. The level of membrane-bound ATP apparently is decreased when Na is added and this decrease is inhibited by strophanthidin. When further syntehsis of [32P]ATP is blocked by the addition of unlabeled Pi, all of the membrane-bound [32P]ATP is dissipated by the addition of Na. Membrane-bound glycolytic enzymes apparently synthesize ATP and deposit it in a membrane-associated compartment from which it is used by the Na/K pump.