title: Properties of Na+, K+-ATPase of liver plasma membranes in the hamster.
abstract: This study was designed to establish the properties of liver plasma membranes (LPM) Na+,K+-ATPase in the hamster and to determine whether a similar assay may be used to measure enzyme activity in the hamster and in the rat. Maximal Na+,K+-ATPase activity was obtained when the assay medium contained 5 mM Mg APT2- with or without 1 mM free Mg2+, 120 mM Na+, 12,5 mM K+. The incubation must be performed at 37 degrees C, pH 7.4. In the absence of free Mg2+, the saturation curve with respect to the substrate Mg ATP2- resulted in biphasic complex kinetics with a maximal activity at a substrate concentration of 5 mM. In the presence of 1 mM free Mg2+ activation of Na+,K+-ATPase and modification of the kinetics were observed: the biphasic curve tended to disappear and to become of the Michaelis-Menten type. The apparent Km for Mg APT2- was 0.36 mM and the Vmax 34.5 mumol.h-1.mg protein-1. In the presence of 10 mM free Mg2+ a decrease in the Vmax was observed without any effect on the apparent Km for Mg APT2-. It is concluded that the same incubation medium may be used to assay LPM N+,K+-ATPase from hamster and rat and that the addition of 1 mM free Mg2+ to the incubation medium is recommended to obtain Michaelis-Menten kinetics in order to eliminate complex kinetics due to the absence of free Mg2+.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D006224:Cricetinae / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008099:Liver / Q000201:enzymology*; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D008647:Mesocricetus / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013696:Temperature
chemical_list: D010042:Ouabain; D000255:Adenosine Triphosphate; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D008274:Magnesium; D011188:Potassium