The base-exchange enzyme activities of sarcolemma and sarcoplasmic reticulum from rat heart.
The Ca2+ dependent incorporation of [14C]ethanolamine, L-[14C]serine and [14C]choline into phosphatidylethanolamine, phosphatidylserine and phosphatidylcholine, respectively, were investigated in membrane preparations from rat heart. The ethanolamine and serine base-exchange enzyme-catalyzed reactions were associated with the sarcolemma and sarcoplasmic reticulum. There was a 17.2-fold and 6.8-fold enrichment, respectively, of the serine and the ethanolamine base-exchange enzyme activities in the sarcolemma compared to the starting whole homogenate. The sarcoplasmic reticulum was enriched in the ethanolamine and serine base-exchange enzyme activities. The choline base-exchange enzyme activity of all membranes fractions was negligible compared to the ethanolamine or serine base-exchange enzyme activities. The apparent Km for the ethanolamine and serine base-exchange enzyme in sarcolemma was 14 microM and 25 microM, respectively. The pH optimum for these base-exchange activities was 7.5-8.0. There was a dependence upon Ca2+ for these reactions with a 1 or 4 mM concentration required for maximal activity. The properties of the sarcoplasmic reticulum base-exchange enzymes were similar to the sarcolemmal base-exchange enzymes.
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D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002794:Choline / Q000378:metabolism; D019856:Ethanolamine; D004983:Ethanolamines / Q000378:metabolism; D007700:Kinetics; D009206:Myocardium / Q000201:enzymology*; D019884:Nitrogenous Group Transferases; D010743:Phospholipids / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012508:Sarcolemma / Q000201:enzymology*; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D012694:Serine / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D014018:Tissue Distribution; D014166:Transferases / Q000378:metabolism*
D004983:Ethanolamines; D010743:Phospholipids; D012694:Serine; D019856:Ethanolamine; D014166:Transferases; D019884:Nitrogenous Group Transferases; C022370:phospholipid serine base exchange enzyme; D000254:Sodium-Potassium-Exchanging ATPase; D002794:Choline; D002118:Calcium