KINETICS OF CU2+ INHIBITION OF NA+ K+-ATPASE

The interaction of Cu2+ With enzymatic activity of rabbit kidney Na+/K +-ATPase was studied in media with buffered, defined free Cu2+ levels. The IC50-values are 0.1 mu mol/l for Na+/K-ATPase and 1 mu mol/l for K+-pNPPase. Dithiothreitol (DTT) reverses the inhibitory effect of Cu2 + in vitro. Cu2+ exerts non-competitive effects on the enzyme with res pect to Na+, K+, ATP or pNPP, but has a mixed-type inhibitory effect w ith respect to Mg2+. It is concluded that the appreciation of the inhi bitory effect of CU2+ on this enzyme requires carefully composed assay media that include a buffer for Cu2+, and that the IC50-values calcul ated according to this model indicate that CU2+ may be more toxic than previously anticipated.