ACTIVATION OF CTP-PHOSPHOCHOLINE CYTIDYLYLTRANSFERASE BY HYPOCHLORITE-OXIDIZED PHOSPHATIDYLCHOLINES

CTP:phosphocholine cytidylyltransferase (CT) catalyzes a rate-limiting , regulatory step in mammalian biosynthesis of phosphocholine (PC). An ionic phospholipids, fatty acids and diacylglycerol activate CT and pr omote its intercalation into the lipid bilayer, whereas zwitterionic p hospholipids such as phosphatidylcholines do not, We investigated the effectiveness of polyunsaturated phosphatidylcholines as CT activators after hypochlorite oxidation. Detection and quantitation of oxidized PCs were evaluated by thin layer chromatography, high performance liqu id chromatography, and conjugated dienes. Purified CT was assayed in t he presence of multilamellar vesicles, containing variable concentrati ons of oxidized and parent PCs. The results demonstrate that particula r species of oxidized PCs activate CT as potently as anionic lipids. T he greater the number of double bonds available for oxidation in the f atty acid at the sn-2 position of the PC, the more effective was the o xidized PC as an activator of CT. Oxidized phospholipids at 1:1 bleach /lipid activated CT in the following order: PAPC > PL3PC > PL2PC compa red to unoxidized controls. Since oxidized phospholipids decrease bila yer order (M.L. Wratten et al., Biochemistry 31 (1992) 10901-10907) th ese results are consistent with the activation of CT by perturbations of lipid bilayer packing. (C) 1998 Published by Elsevier Science B.V. All rights reserved.