Phosphatidate phosphohydrolase in purified rat brain myelin.

Highly purified myelin from rat brain stem has been shown to contain phosphatidate phosphohydrolase, an enzyme which converts phosphatidate to diacylglycerol. The high levels relative to cytosol and microsomes (17% and 22%, respectively) tended to preclude contamination by these fractions as the source of activity. Additional evidence came from study of repeated purification, mixing experiments, and washing of the myelin with salt and detergent. We conclude that this enzyme, in addition to being widely distributed in other subcellular fractions, is intrinsic to the myelin membrane. Through its activity it generates a key substrate for the cytidine (Kennedy) pathway which was previously shown to occur in this membrane.