OUABAIN SENSITIVE NA+/K+-TRANSPORTING ATPASE FROM THE BRAIN OF POEKILOCERUS BUFONIUS

1. The properties of Na+/K+-transporting ATPase in microsomal fractions from the nervous tissue of the grasshopper, Poekilocerus bufonius were investigated. 2. Two components of ATPase activity are present. 3. Inclusion of 1 mM ouabain in the incubation media reduced the activity of total and Na+/K+-ATPase by 57 and 79%, respectively. 4. The maximum velocity (V(max)) was decreased by the addition of 1 mM ouabain, whereas the apparent K(m) value was not affected indicating a non-competitive type of inhibition. 5. The calculated value of the pI50 was 6.4 (I50 = 3.98 x 10(-7) M) for ouabain inhibition of the enzyme showing great sensitivity to the cardiac glycoside ouabain. 6. The present results show that the physicochemical properties of Na+/K+-transporting ATPase from the brain of P. bufonius are essentially the same as for the enzyme prepared from the excretory system of the insect which has been previously investigated. 7. Dissimilarities were also observed between these tissues in the way that the enzyme from the brain was sensitive to ouabain inhibition with a non-competitive type rather than a ouabain-resistance and a competitive type of inhibition for the enzyme from the excretory system. 8. These dissimilarities are probably due to different isoenzyme patterns available in the same insect.