On the specificity of cytidine diphosphate diglycerides in monophosphoinositide biosynthesis by rat brain preparations

Abstract

Some properties of the enzyme cytidine diphosphate diglyceride : inositol transferase which catalyzes the reaction[Formula: see text]have been studied with various preparations from rat brain. The enzyme was found to be primarily located in the microsomal fraction (either the 12 000 × g supernatant or the 90 000 × g pellet). Optimal conditions were established for pH and concentrations of each of the reactants and Mn2+ ion. A number of cytidine diphosphate diglycerides with different fatty acids in the 1- and 2-positions were synthesized chemically and used as substrates for the above reaction. The substrates included those with the following distribution of fatty acids: 1,2-dipalmitoyl; 1,2-distearoyl; 1-palmitoyl,2-oleoyl; 1-stearoyl,2-oleoyl; 1-oleoyl,2-stearoyl and 1,2-dioleoyl. It was observed that those substrates with oleic at the 2-position were more readily utilized than those containing palmitic or stearic acids at the 2-position or at both the 1- and 2-positions. This selectivity for cytidine diphosphate diglyceride with an unsaturated fatty acid at the 2-position was consistent with the pattern of fatty acid distribution found for isolated rat brain monophosphoinositide. In the latter, saturated fatty acids (stearic and palmitic acids) were predominantly located at the 1-position and unsaturated fatty acids (20:4, arachidonic acid) were predominantly located in the 2-position.