Properties of energy-dependent calcium transport by rat liver microsomal fraction as revealed by initial-rate measurements.
Measurements of the initial rate of Ca2+ transport by rat liver microsomal preparations reveal the existence of two phases of transport activity. The first, a phase of rapid transport, is complete by 3-5 min, at which time the second (slower) phase begins; this remains linear for up to at least 40 min. The initial phase is minimal in the absence of MgATP. The initial rate of Ca2+ transport reaches values as high as 25 nmol/min per mg of protein; the Km for Ca2+total is 1-2 micrometer and that for MgATPtotal about 500 micrometer. Ruthenium Red (3-5 nmol/mg of protein) has little effect on the initial rate of transport, whereas tributylin (2 micrometer) inhibits equally in a KC1- or a KNO3-containing medium. Compunds that  collapse components of the proton electrochemical gradient in mitochondria (valinomycin and carbonyl cyanide m-chlorophenylhydrazone) each inhibit by 70-80% the initial rate of microsomal Ca2+ transport.
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D008862:Microsomes, Liver / Q000378:metabolism*; D051381:Rats; D012430:Ruthenium Red / Q000494:pharmacology; D014220:Trialkyltin Compounds / Q000494:pharmacology; D014634:Valinomycin / Q000494:pharmacology
D014220:Trialkyltin Compounds; D012430:Ruthenium Red; D014634:Valinomycin; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D000255:Adenosine Triphosphate; D008274:Magnesium; D002118:Calcium