DDT inhibition of (Na+, K+)-activated ATPase in gill tissue of Fundulus heteroclitus

The DDT i nh ibition of (Na+, K+) a ctivated ATPase in gill pre parations of the euryhaline teleost , Fundulus heteroclitus, was measured. The (Na+, K+) -activate d ATPase was found to be sensitive to DDT, with 74.6% of the e nzyme's specific activity inhibited by 20 ppm DDT . The (Mg++)-activated ATPase was also sensitive to inhibition bv DDT but not to the extent of the (Na+, K+) activat ed ATPase . Due to p revious work which showed that DDT antagonized valinomycin-induced K+ conductance in a synthetic membrane, the effect of K+ on DDT inh ibi tion was examined kinetically. Th~ ~m for K+ in gill preparations treated with 5 ppm .DDT was greater than the~ of the control, indicating t ha t DDT i nhibi tion o f (Na+, K+)act ivated ATPase involves alteration of the aff ini ty of the enzyme fo r K+.