The temperature dependence of activation by phosphatidylserine of the sodium pump adenosine triphosphatase.

1. Treatment of rabbit brain homogenates with deoxycholate reduced ouabain-insensitive ATPase sixfold and subsequently adding phosphatidylserine had no effect. Ouabain-sensitive ATPase was made entirely latent but it was fully restored on adding phosphatidylserine.2. Temperature and pH were varied to see if the reconstituted system resembled that in the original membranes. Linear Arrhenius plots were always obtained with the homogenate, and the activation energy was higher for the ouabain-sensitive than for the ouabain-resistant enzyme.3. A break at about 15 degrees C was found in the Arrhenius plot of the reconstituted enzyme, but there was no break without added phosphatidylserine or when ouabain was added. The break suggests that the conformation and catalytic activity of the enzyme protein depended on the physical state of phosphatidylserine.