Effect of phospholipid on substrate phosphorylation by a catalytic fragment of protein kinase C

Limited tryptic digestion of protein kinase C purified from mouse brain generated a 36-kDa fragment which no longer required Ca2+ and phospholipid for activity or bound phorbol ester. Under appropriate conditions, the isolated fragment was stable for several months at 4 degrees C or upon freezing and storage at -70 degrees C. Kinetic characteristics of the fragment were similar to those for the intact protein kinase. Although the fragment did not require phospholipid for activity, anionic phospholipids affected the extent of its activity in a pH-, substrate-, and substrate concentration-dependent manner. This effect appeared to be due to complex formation between the phospholipid and substrate. The catalytic fragment thus permits detection of a second point of interaction of phospholipid with the protein kinase C system in addition to the already described phospholipid regulatory domain.