Calcium-binding protein regucalcin is an activator of (Ca2+-Mg2+)-adenosine triphosphatase in the plasma membranes of rat liver

The effect of regucalcin, a calcium-binding protein isolaetd from rat liver cytosol, on (Ca2+-Mg2+)-adenosine triphosphatase (ATPase) activity in the plasma membranes of rat liver was investigated. 125I-Regucalcin bound to the plasma membranes in the presence or absence of 0.1 mM Ca2+. Regucalcin (0.35 μM) increased the plasma membrane (Ca2+-Mg2+)-ATPase activity about 15% (p M), glucagon (10-6 and 10-5M) or norepinephrine (10-7-10 M), suggesting that the regucalcin effect is not linked to guanosine triphosphate (GTP)-binding protein in the plasma membranes. Vanadium (10 and 10 μM), which inhibits the phosphorylation of liver plasma membrane (Ca2+-Mg2+)-ATPase, decreased the enzyme activity about 20% (p