Demonstration of the phosphorylated intermediates of the Ca2+-transport ATPase in a microsomal fraction and in a (Ca2+ + Mg2+)-ATPase purified from smooth muscle by means of calmodulin affinity chromatography.
Ca2+ -dependent hydroxylamine-sensitive phosphorylated proteins can be demonstrated in a microsomal fraction of porcine antrum (stomach) smooth muscle and in a Ca2+ -transport ATPase ((Ca2+ + Mg2+)-ATPase) purified from this tissue by means of a calmodulin affinity technique. These phosphoproteins represent the phosphorylated intermediates of the (Ca2+ + Mg2+)-ATPases. In the (Ca2+ + Mg2+)-ATPase purified from smooth muscle the phosphorylated intermediate has an Mr of 130000 corresponding to the value found for erythrocyte (Ca2+ + Mg2+)-ATPase. In the smooth muscle microsomal fraction this 130 kDa phosphoprotein can also be seen, although its intensity is usually very low compared to a corresponding phosphorylation at Mr 100000. Including La3+ together with Ca2+ during phosphorylation of the microsomes increased selectively the steady state-level of the 130 kDa phosphoprotein over the value of the 100 kDa one. The 100 kDa Ca2+ -dependent phosphoprotein could either indicate the presence of a (Ca2+ + Mg2+)-ATPase of the same type of sarcoplasmic reticulum of skeletal muscle, or it could represent a proteolytic product of the 130 kDa phosphoprotein.
D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases / Q000302:isolation & purification / Q000378:metabolism*; D002147:Calmodulin; D002846:Chromatography, Affinity; D007811:Lanthanum / Q000494:pharmacology; D008861:Microsomes / Q000201:enzymology*; D008970:Molecular Weight; D009130:Muscle, Smooth / Q000201:enzymology*; D013270:Stomach / Q000201:enzymology; D013552:Swine
D002147:Calmodulin; D007811:Lanthanum; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases