The Neurospora plasma membrane Ca2+ pump.

Plasma membrane vesicles isolated from the eukaryotic microorganism Neurospora crassa by the concanavalin A method catalyze Mg2+-ATP dependent 45Ca2+ accumulation. Since the ATP-responsive vesicles are functionally inverted, the Ca2+ transport system presumably operates as a Ca2+ exit pump in the intact cell. The mechanism of the Ca2+ pump system involves two components: 1) an electrogenic, proton-translocating ATPase (EC 3.6.1.3), which utilizes the chemical energy of ATP hydrolysis to generate a transmembrane electrical potential and pH gradient, and 2) a Ca2+/H+ antiporter, which utilizes the transmembrane pH gradient to energize the active transport of Ca2+. Evidence for this mechanism is presented and the possible implications of these findings for the mechanisms of Ca2+ pumps in other cells are discussed.