[Characterization of changes in the activity of K+-n-nitrophenylphosphatase of erythrocyte ghosts under the influence of ouabain].

Variation of K+-p-NPP-ase of human ghosts under the action of ouabain (10(-11)-10(-3) M) has been studied. In human ghosts the activity of ouabain-sensitive K+-p-NPP-ase has been found to make up 65% of the total enzyme activity. The activity of ouabain-sensitive K+-p-NPP-ase reaches a maximum level at pH 7.6-8.0. A decrease in the activity of this enzyme caused by ouabain is of two-phase character. In the range of ouabain concentration from 10(-10) M to 10(-6) M and from 10(-5) M to 10(-3) M the enzyme activity lowers significantly; in the range of 10(-7) M to 10(-5) M it reaches the plato. Two types of the enzyme are assumed to exist differing by 4-5 orders of magnitude in their sensitivity to ouabain, inhibitor affinity constants and Michaelis constants.