title: Calcium inhibition of rat liver microsomal calcium-dependent ATPase.
abstract: Measurement of the inward rate of Ca2+ transport by rat liver microsomes under conditions of varying free intravesicular Ca2+ (1 microM to 5 mM) revealed that inward transport rate is maximum at low intravesicular Ca2+, and that transport rate decreases with an apparent inhibition constant of about 250-350 microM as intravesicular Ca2+ accumulates. This relationship is confirmed by measurement of Ca2+-dependent ATPase activity; activity is greatest when intravesicular Ca2+ is 1 microM, is lower when intravesicular Ca2+ is 60 microM, and is minimum when intravesicular Ca2+ is 5 mM. Unexpectedly, the ratio of Ca2+ transport rate to Ca2+-dependent ATP hydrolysis rate appears to be significantly greater than 2:1.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors*; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D010070:Oxalates / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D010070:Oxalates; D000252:Calcium-Transporting ATPases; D002118:Calcium