Distribution and properties of CDP-diglyceride:inositol transferase from brain.

CDP-diglyceride is converted to phosphatidyl inositol by several particulate subcellular fractions of guinea pig brain, with highest specific activity in the microsornal fraction. Optimal conditions with respect to pH, metal ion concentration, and substrate concentrations have been determined. The reaction was stimulated by the addition of bovine serum albumin and by Tween 80. Of several DL-CDP-diglycerides synthesized and used as substrates in a spectrophotometric assay for the enzyme, DL-CDP-didecanoin was the most active. The enzyme showed a high selectivity for myo-inositol. Of a number of compounds tested, only scyllo-inosose and epi-inosose served as substrates. Three inositol isomers and three myo-inositol monophosphates inhibited the reaction slightly. The most potent inhibitor found was galactinol, a myo-inositol galactoside. THE ENZYME CDP-diglyceride : inositol transferase (CDP-diglyceride : inositol 1,2diglyceride phosphotransferase, EC 2.7.8) catalyses the reaction: CDP-diglyceride + myo-inositol+ phosphatidyl inositol + CMP The occurrence of this reaction in brain is well-documented (AGRANOFF, BRADLEY and BRADY, 1958; THOMPSON, STRICKLAND and ROSSITER, 1963). Phosphatidyl inositol is the precursor of the diand tri-phosphoinositides (FOLCH, 1949; BROCKERHOFF and BALLOU, 1962; ROSSITER and PALMER, 1965), which are found predominantly in brain (DAWSON and EICHBERG, 1965). The enzymatic conversion of phosphatidyl inositol to diphosphoinositide by ATP was demonstrated in brain (COLODZIN and KENNEDY, 1964) and in guinea pig liver mitochondria (HAJRA, SEIFFERT and AGRANOFF, 1965). A recent study of developmental changes in rat brain enzymes concerned with inositol lipid metabolism showed that the increase in CDP-diglyceride : inositol transferase activity was not associated exclusively with any period of development, while phosphatidyl inositol kinase activity rose before myelination, and diphosphoinositide kinase and triphosphoinositide monoesterase activities rose during myelination (SALWAY, HARWOOD, KAI, WHITE and HAWTHORNE, 1968). The rapid turnover of This investigation was supported in part by research grant NB-3101 from the National Institutes of Health. A preliminary report was given at the Federation of Western Societies of Neurological Science, 1-3 March, 1968, San Diego, California. * Supported by trainee grant 2-TI-GM-187-06 and predoctoral fellowship PHS416-4 from the National Institutes of Health. The experimental data in this paper are taken from a dissertation submitted by J. Benjamins to the University of Michigan in partial fulfillment of the requirements for the Ph.D. degree (1967). Present address: Department of Neurology, School of Medicine, Johns Hopkins University, Baltimore, Maryland. Department of Biochemistry and Mental Health Research Institute,