Stimulatory effect of regucalcin on ATP-dependent Ca(2+) uptake activity in rat liver mitochondria.
The effect of Ca(2+)-binding protein regucalcin on Ca(2+)-ATPase activity in isolated rat liver mitochondria was investigated. The presence of regucalcin (0.1, 0.25, and 0.5 microM) in the enzyme reaction mixture led to a significant increase in Ca(2+)-ATPase activity. Regucalcin significantly stimulated ATP-dependent (45)Ca(2+) uptake by the mitochondria. Ruthenium red (10(-5) M) or lanthanum chloride (10(-4) M), an inhibitor of mitochondrial Ca(2+) uptake, completely inhibited regucalcin (0.25 microM)-increased mitochondrial Ca(2+)-ATPase activity and (45)Ca(2+) uptake. The effect of regucalcin (0.25 microM) in increasing Ca(2+)-ATPase activity was completely inhibited by the presence of digitonin (10(-2)%), a solubilizing reagent of membranous lipids, or vanadate (10(-5) M), an inhibitor of phosphorylation of ATPase. The activatory effect of regucalcin (0.25 microM) on Ca(2+)-ATPase activity was not further enhanced in the presence of dithiothreitol (2.5 mM), a protecting reagent of the sulfhydryl (SH) group of the enzyme, or calmodulin (0.60 microM), a modulator protein of Ca(2+) action that could increase mitochondrial Ca(2+)-ATPase activity. The present study demonstrates that regucalcin can stimulate Ca(2+) pump activity in rat liver mitochondria, and that the protein may act on an active site (SH group)-related to phosphorylation of mitochondrial Ca(2+)-ATPase.
Takahashi
H
H
Laboratory of Endocrinology and Molecular Metabolism, Graduate School of Nutritional Sciences, University of Shizuoka, Japan.
Yamaguchi
M
M
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000494:pharmacology*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002147:Calmodulin / Q000494:pharmacology; D002265:Carboxylic Ester Hydrolases; D047908:Intracellular Signaling Peptides and Proteins; D007700:Kinetics; D007811:Lanthanum / Q000494:pharmacology; D008297:Male; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012430:Ruthenium Red / Q000494:pharmacology; D015238:Sulfotransferases; D014638:Vanadates / Q000494:pharmacology
D002135:Calcium-Binding Proteins; D002147:Calmodulin; D047908:Intracellular Signaling Peptides and Proteins; C028521:lanthanum chloride; D012430:Ruthenium Red; D014638:Vanadates; D007811:Lanthanum; D000255:Adenosine Triphosphate; D015238:Sulfotransferases; C028152:alcohol sulfotransferase; D002265:Carboxylic Ester Hydrolases; C513325:Rgn protein, rat; D000252:Calcium-Transporting ATPases; D002118:Calcium