Activation of Hepatic Microsomal Ca2+-Adenosine Triphosphatase by Calcium-Binding Protein Regucalcin

Abstract

The effect of regucalcin, a calcium-binding protein isolated from rat liver cytosol, on Ca2+-adenosine triphosphatase (ATPase) activity in hepatic microsomes was investigated. Mg2+-ATPase activity was clearly increased by the presence of 50 μm Ca2+. Regucalcin (1.0—4.0μM) caused a remarkable elevation (about 3-fold) of Ca2+-ATPase activity. Also, Mg2+-ATPase activity was increased (about 1.6-fold) by the presence of regucalcin (2.0 and 4.0 μM). Guanosine-5'-0-(3-thiotriphosphate) (GTP,s; 10-5 and 10-4M) and nicotinamide adenine dinucleotide phosphate oxidized form (NADP+; 10 -5 to 10-3M) or reduced form (NADPH; 10 -4 and 10-3M) significantly increased Ca2+-ATPase activity. These increases were not enhanced by the presence of regucalcin (2.0 μM). of various metal ions, a comparatively low concentration of V5+ (10-5M) or Cd2+ (10 -6M) significantly increased Ca2+-ATPase activity, while Hg2+, Zn2+, Cu2+ and Mn2+ did not have such an effect. Regucalcin (2.0 μM) did not enhance the effect of V5+ and Cd2+ on Ca2+-ATPase activity. The present finding, that regucalcin activates hepatic microsomal Ca2+-ATPase, suggests a cell physiological role of regucalcin as an activator in the microsomal Ca2+ -pump activity. This action of regucalcin may not be influenced by other regulators. © 1989, The Pharmaceutical Society of Japan. All rights reserved.