(Ca2+ + Mg2+)-ATPase in enriched sarcolemma from dog heart.
An enriched fraction of plasma membranes was prepared from canine ventricle by a process which involved thorough disruption of membranes by vigorous homogenization in dilute suspension, sedimentation of contractile proteins and mitochondria at 3000 X g followed by sedimentation of a microsomal fraction at 200 000 X g. The microsomal suspension was then fractionated on a discontinuous sucrose gradient. Particles migrating in the density range 1.0591--1.1083 were characterized by (Na+ + K+)-ATPase activity and [3H]ouabain binding as being enriched in sarcolemma and were comprised of nonaggregated vesicles of diameter approx. 0.1 micron. These fractions contained (Ca2+ + Mg2+)-ATPase which appreared endogenous to the sarcolemma. The enzyme was solubilized using Triton X-100 and 1 M KCl and partially purified. Optimal Ca2+ concentration for enzyme activity was 5--10 microM. Both Na+ and K+ stimulated enzyme activity. It is suggested that the enzyme may be involved in the outward pumping of Ca2+ from the cardiac cell.
D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002458:Cell Fractionation; D002462:Cell Membrane / Q000201:enzymology; D004285:Dogs; D008274:Magnesium / Q000494:pharmacology; D009206:Myocardium / Q000201:enzymology*; D011188:Potassium / Q000494:pharmacology; D012508:Sarcolemma / Q000201:enzymology*; D012964:Sodium / Q000494:pharmacology
D012964:Sodium; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D011188:Potassium