title: Localization of (Ca2+ + Mg2+)-ATPase, Ca2+ pump and other ATPase activities in cardiac sarcolemma.
abstract: N-Ethylmaleimide was employed as a surface label for sarcolemmal proteins after demonstrating that it does not penetrate to the intracellular space at concentrations below 1.10(-4) M. The sarcolemmal markers, ouabain-sensitive (Na+ +K+)-ATPase and Na+/Ca2+-exchange activities, were inhibited in N-ethylmaleimide perfused hearts. Intracellular activities such as creatine phosphokinase, glutamate-oxaloacetate transaminase and the internal phosphatase site of the Na+ pump (K+-p-nitrophosphatase) were not affected. Almost 20% of the (Ca2+ +Mg2+)-ATPase and Ca2+ pump were inhibited indicating the localization of a portion of this activity in the sarcolemma. Sarcolemma purified by a recent method (Morcos, N.C. and Drummond, G.I. (1980) Biochim. Biophys. Acta 598, 27-39) from N-ethylmaleimide-perfused hearts showed loss of approx. 85% of its (Ca2+ +Mg2+-ATPase and Ca2+ pump compared to control hearts. (Ca2+ +Mg2+)-ATPase and Ca2+ pump activities showed two classes of sensitivity to vanadate ion inhibition. The high vanadate affinity class (K1/2 for inhibition approx. 1.5 microM) may be localized in the sarcolemma and represented approx. 20% of the total inhibitable activity in agreement with estimates from N-ethylmaleimide studies. Sucrose density fractionation indicated that only a small portion of Mg2+-ATPase and Ca2+-ATPase may be associated with the sarcolemma. The major portion of these activities seems to be associated with high density particles.
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D005033:Ethylmaleimide; D007473:Ion Channels / Q000378:metabolism; D008929:Mitochondria, Heart / Q000201:enzymology; D009206:Myocardium / Q000201:enzymology; D011817:Rabbits; D012508:Sarcolemma / Q000201:enzymology* / Q000648:ultrastructure; D012519:Sarcoplasmic Reticulum / Q000201:enzymology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D014639:Vanadium / Q000494:pharmacology
chemical_list: D007473:Ion Channels; D014639:Vanadium; D009597:4-Nitrophenylphosphatase; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase; D005033:Ethylmaleimide; D002118:Calcium