title: Ca2+ transporting activity of membrane fractions isolated from the post-mitochondrial supernatant of rat liver.
abstract: The post-mitochondrial supernatant of rat liver contains two vesicular fractions which transport Ca2+ actively. The heavier fraction, sedimenting at 17.500 xg, 20 min, is enriched in plasma membrane markers and apparently contains both a Ca2+ pumping ATPase and a Na+/Ca2+ exchanger. These activities have been attributed to the plasma membrane vesicles. The lighter fraction, sedimenting at 100.000 xg, 60 min, is enriched in endoplasmic reticulum markers, and contains only a Ca2+ pumping ATPase, which can be differentiated from that of the heavier fraction on the basis of the sensitivity to vanadate. The Ca2+ pumping activity of endoplasmic reticulum appears to be regulated by both a cAMP-dependent, and a calmodulin-dependent system. The former system involves a heat-stable protein fraction from the cytosol. The regulation by the cAMP and the calmodulin-dependent systems involves the phosphorylation of several proteins in the endoplasmic reticulum membrane.
mesh_terms: D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008297:Male; D008928:Mitochondria / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000494:pharmacology; D013367:Submitochondrial Particles / Q000378:metabolism*; D014268:Trifluoperazine / Q000494:pharmacology; D014638:Vanadates; D014639:Vanadium / Q000494:pharmacology
chemical_list: D002147:Calmodulin; D014639:Vanadium; D014268:Trifluoperazine; D014638:Vanadates; D012964:Sodium; D000242:Cyclic AMP; D002118:Calcium