An endogenous inhibitor protein of synaptic plasma membrane (Ca2+ + Mg2+)-ATPase.
An inhibitor protein of synaptic plasma membrane (Ca2+ + Mg2+)-ATPase was purified to apparent homogeneity from rat cerebrum by a molecular weight cut followed by chromatography of cytosol proteins with molecular weights between 10 000 and 3500 on DEAE-Sephadex at pH 5.2. The inhibitor could be partially inactivated by proteinases and dithiothreitol, but was heat-stable. Gel filtration gave a molecular weight of about 6000. Like the (Ca2+ + Mg2+)-ATPase inhibitor protein isolated from erythrocytes, the inhibitor from brain contains a characteristic high proportion of glutamic acid (36%) and glycine (37%) residues. Synaptic plasma membrane Mg2+-ATPase and microsomal membrane (Ca2+ + Mg2+)-ATPase did not respond to the inhibitor. Synaptic plasma membrane and erythrocyte membrane (Ca2+ + Mg2+)-ATPases, however, were affected. Inhibitory influence on synaptic membrane (Ca2+ + Mg2+)-ATPase was reversible, since inhibition could be relieved upon removal of inhibitor from saturable sites on the membrane. The inhibitor is not a calmodulin-binding protein, since the concentration of calmodulin for half-maximal activation of the ATPase was unaffected by its presence. Mode of inhibition of the (Ca2+ + Mg2+)-ATPase by the inhibitor was non-competitive.
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D000818:Animals; D001923:Brain Chemistry; D017301:Ca(2+) Mg(2+)-ATPase / Q000037:antagonists & inhibitors*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D004229:Dithiothreitol / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000302:isolation & purification*; D006358:Hot Temperature; D008297:Male; D008970:Molecular Weight; D051381:Rats; D011919:Rats, Inbred Strains; D013570:Synaptic Membranes / Q000201:enzymology*
D004791:Enzyme Inhibitors; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D004229:Dithiothreitol