Phosphatidylcholine enhances the activity of rat liver type II phosphatidylinositol-kinase

In English A PtdIns 4-kinase was purified extensively from rat liver exocytotic vesicles. The enzyme had a low Km 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 enhanced several-fold by PtdCho, and to some extent by other phospholipids with basic polar head groups, and was inhibited by PtdSer. Kinetic analyses, presenting the substrate in mixed micelles of Triton X-100, PtdIns and PtdCho, showed that the effect of PtdCho was both to increase Vmax and to decrease the apparent Km for micellar PtdIns.