A Ca2(+)-activated, Mg2(+)-dependent ATPase with high affinities for both Ca2+ and Mg2+ in vascular smooth muscle microsomes: comparison with plasma membrane Ca2(+)-pump ATPase.
A Ca2(+)-ATPase with a high affinity for free Ca2+ (apparent Km of 0.13 microM) was found and characterized in membrane fractions from porcine aortic and coronary artery smooth muscles in comparison with the plasma membrane Ca2(+)-pump ATPase purified from porcine aorta by calmodulin affinity chromatography. The activity of the high-affinity Ca2(+)-ATPase became enriched in a plasma membrane-enriched fraction, suggesting its localization in the plasma membrane. The enzyme was fully active in the absence of exogenously added Mg2+, but required a minute amount of Mg2+ for its activity as evidenced by the findings that it was fully active in the presence of 0.1 microM free Mg2+ but lost the activity in a reaction mixture containing trans-cyclohexane-1,2-diamine-N,N,N',N'-tetraacetic acid as a divalent cation chelator which has, unlike EGTA, high affinities for both Ca2+ and Mg2+. It was able to utilize a variety of nucleoside di- and triphosphates as substrates, such as ADP, GDP, ATP, GTP, CTP, and UTP, showing a broad substrate specificity. The activity of the enzyme was not modified by calmodulin (5, 10 micrograms/ml). Trifluoperazine, a calmodulin antagonist, had a partial inhibitory effect on the activity at 30 to 240 microM, but this inhibition could not be reproduced by a more specific calmodulin antagonist, W-7, indicating that this inhibition by trifluoperazine was not specific. Furthermore, the high-affinity Ca2(+)-ATPase activity was not modified either by low concentrations (0.5-9 microM) of vanadate or by 1-100 microM p-chloromercuribenzoic acid. Cyclic GMP, nitroglycerin, and nicorandil did not have any effect on the enzyme activity.(ABSTRACT TRUNCATED AT 250 WORDS)
Sun
H T
HT
Department of Pharmacology, Niigata University School of Medicine.
Yoshida
Y
Y
Imai
S
S
D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000201:enzymology; D002118:Calcium / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000201:enzymology*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002147:Calmodulin / Q000494:pharmacology; D002462:Cell Membrane / Q000201:enzymology; D002729:Chloromercuribenzoates / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology*; D008861:Microsomes / Q000201:enzymology*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000201:enzymology*; D009711:Nucleotides / Q000378:metabolism; D013379:Substrate Specificity; D013449:Sulfonamides / Q000494:pharmacology; D013552:Swine; D014638:Vanadates / Q000494:pharmacology; D020245:p-Chloromercuribenzoic Acid
D015220:Calcium Channels; D002147:Calmodulin; D002729:Chloromercuribenzoates; D009711:Nucleotides; D013449:Sulfonamides; D014638:Vanadates; D004533:Egtazic Acid; D020245:p-Chloromercuribenzoic Acid; C017967:W 7; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D002118:Calcium