PHOSPHATIDYLCHOLINE ENHANCES THE ACTIVITY OF RAT-LIVER TYPE-II PHOSPHATIDYLINOSITOL-KINASE

A PtdIns 4-kinase was purified extensively from rat liver exocytotic v esicles. The enzyme had a low K(m) for ATP, was inhibited by adenosine , and had an apparent molecular mass of 54 kDa, indicating it to be a type II PtdIns-kinase. The activity of the purified enzyme was enhance d several-fold by PtdCho, and to some extent by other phospholipids wi th basic polar head groups, and was inhibited by PtdSer. Kinetic analy ses, presenting the substrate in mixed micelles of Triton X-100, PtdIn s and PtdCho, showed that the effect of PtdCho was both to increase V( max) and to decrease the apparent K(m) for micellar PtdIns.