The triphosphoinositide phosphodiesterase of brain tissue

Abstract

Triphophoinositide phosphodiesterase free from phosphomonesterase activity was isolated from ox brain. The enzyme removed diglyceride only from triphosphoinositide and diphosphoinositide. No absolute requirement for metal ions was found, but the dialysed enzyme was inhibited by 0.5 m[image]-EDTA. Hydrolysis of triphosphoinositide was limited unless a cationic amphipathic substance was present as activator. Histone, protamine, Ca2+ ions and Mg2+ ions also activated at certain concentrations. Sodium chloride in the presence of lecithin or phosphatidylethanolamine produced a marked activation; the phospholipids alone did not. Anionic amphipathic substances were potent inhibitors of the enzyme. It is suggested that the activators produce their effect by decreasing the excess of negative charge on the phosphate groups of the substrate molecule which allows the enzyme to come into to a favourable stereochemical orientation.