Effect of Mg2+ and spermine on the kinetics of Ca2+ transport in rat-liver mitochondria.
Plots relating the initial rate of mitochondrial Ca2+ transport to the Ca2+ concentration (kinetic plots) have a hyperbolic shape in a Ca2+ concentration range of 2.5-100 muM as measured in sucrose or KCl media. In the presence of Mg2+ or a polyamine spermine, which both are competitive inhibitors of Ca2+ binding to low affinity sites at the membrane surface, the shape of the plots becomes sigmoidal. At higher concentrations of these agents linear kinetic plots are obtained as measured in a sucrose medium. In a KCl medium the sigmoidality of the kinetic plots is enhanced by an increase in the Mg2+ or spermine concentration. It is suggested that Mg2+ and spermine affect the kinetics of Ca2+ transport by interfering with Ca2+ binding to low affinity sites of the membrane surface and that the binding of Ca2+ to these sites is the first step of the mitochondrial Ca2+ transport.
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology*; D008297:Male; D008930:Mitochondria, Liver / Q000378:metabolism*; D051381:Rats; D013096:Spermine / Q000494:pharmacology*
D013096:Spermine; D008274:Magnesium; D002118:Calcium