[Prostaglandin E2 as a lipophilic allosteric modulator of the Na pump]

Curves of inhibition of rat brain Na, K-ATPase and K-pNPPase by prostaglandin E2 (PGE2) showed a sigmoidal shape with nH for PGE2 of 1.4 +/- 0.1 and 1.3 +/- 0.1, respectively. The desensitization of the enzymes with 0.25 M urea (4 degrees, 15 min) caused a loss of their cooperative interaction with PGE2. 2.0 mM PGE2 shifts the temperature break in the Arrhenius plots for the ATPase from 19.8 degrees to 23 degrees and simultaneously increased the Ea below the break by 9.5 kcal/mol. After treatment of the ATPase with phospholipase A2 PGE2 showed no cooperative interaction with the enzyme. Modulation of membrane enzymes by means of the surrounding lipid phasic state appears to be the general mechanism of their indirect allosteric regulation.