Ouabain sensitive Na+/K+-transporting ATPase from the brain of Poekilocerus bufonius

• 1.1. The properties of Na⁺/K⁺-transporting ATPase in microsomal fractions from the nervous tissue of the grasshopper, Poekilocerus bufonius were investigated.
• 2.2. Two components of ATPase activity are present.
• 3.3. Inclusion of 1 mM ouabain in the incubation media reduced the activity of total and Na⁺/K⁺-ATPase by 57 and 79%, respectively.
• 4.4. 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.
• 5.5. The calculated value of the pI₅₀ was 6.4 (I₅₀ = 3.98 × 10^?7M) for ouabain inhibition of the enzyme showing great sensitivity to the cardiac glycoside ouabain.
• 6.6. 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.
• 7.7. 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.
• 8.8. These dissimilarities are probably due to different isoenzyme patterns available in the same insect.