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 mumol/l for Na+/K(+)-ATPase and 1 mumol/l for K(+)-pNPPase. Dithiothreitol (DTT) reverses the inhibitory effect of Cu2+ in vitro. Cu2+ exerts non-competitive effects on the enzyme with respect to Na+, K+, ATP or pNPP, but has a mixed-type inhibitory effect with respect to Mg2+. It is concluded that the appreciation of the inhibitory effect of Cu2+ on this enzyme requires carefully composed assay media that include a buffer for Cu2+, and that the IC50-values calculated according to this model indicate that Cu2+ may be more toxic than previously anticipated.