Properties of Ca2++Mg2+-ATPase from Rat Brain and its Inhibition by Pyrethroids

Ca2++ Mg2+-ATPase from microsomal fractions of rat brain was studied. The enzyme was activated by either Ca2+ or Mg2+ reaching the peak at the Ca2+ concentration of 0.3 mM. Maximal activation occurred at an ATP concentration of 5 mM with an apparent Km of 0.66 mM, a Vmax of 62.5 mol inorganic phosphate/mg protein/hr, and a pH between 8.1 and 8.5. The enzyme was found to be ouabain insensitive but was inhibited by ruthenium red and lanthanum with I50 values of 10-5 and 10-6 M, respectively. The enzyme was highly sensitive to the actions of certain pyrethroid indecticides under in vitro conditions. The cyano-containing pyrethroids, karate and baythroid, exerted a greater inhibitory effect on the enzyme ( Ki = 1.7 and 2 M ) than the non-cyano-containing pyrethroids, permethrin and bioallethrin ( Ki = 7 and 8.5 M )