Abstract
Na+, K+-ATPases were isolated from human kidney medulla and electric organ of Torpedo californica and their enzymatic properties were examined with reference to the sensitivity of the enzyme to ouabain. The specific activity of the purified Na+, K+ -ATPase from human kidney was 93 μmol Pi/mg/h. SDS-polyacrylamide gel electrophoresis revealed that the human enzyme consisted of a and β subunits having molecular weights of approximately 92, 000 and 44, 000, respectively, as the enzymes from other sources. Kd for ouabain of the human enzyme was estimated to be 1.9 nM, while k1 and k-1 of the Torpedo enzyme in the reaction with ouabain were 7.5×10-3s-1m-1 and 0.21×103s-1, respectively. Thus it is apparent that the human enzyme is similar to, but the Torpedo enzyme is different from, the lamb enzyme with respect to their sensitivity to ouabain.
