Characterization of the ouabain-insensitive ATPase activity of rat liver plasma membranes

Very little is currently known about the ouabain-insensitive ATPase activity of the liver plasma membrane; we have therefore characterized it in plasma membranes from rat liver prepared using two different isolation techniques. Greater than 85% of ATPase activity in both preparations was ouabain-insensitive. Based on the effects of multiple inhibitors, including dicyclohexylcarbodiimide (DCCD), N-ethylmaleimide (NEM), vanadate, and oligomycin, the ouabain-insensitive ATPase activity of rat liver plasma membranes consists of a family of ATP-hydrolysing enzymes. Ouabain-insensitive ATPase activity was stimulated by HCO3-in both plasma membranes (13%) and mitochondria (69%) over the range of 7.5 to 9.0, and HCO3--stimulation was similarly inhibited by oligomycin in both preparations. A fraction of the ouabain-insensitive ATPase of liver plasma membranes is inhibited by DCCD and is resistent to inhibition by oligomycin; these characteristics are similar to those of the non-mitochondrial H+-ATPases recently described in lysosomes, endosomes, clathrin-coated vesicles, and Golgi from liver and other cell types.