Studies on the phosphorylcholine of rat liver

LIVER GLYCERYLPHOSPHORYLCHOLINE DIESTERASE 693 the hydrolysis: L-m-GPC+ H20 -+ -glycerophos- phoric acid + choline.3. Similar extracts also attacked L-x-glycerylphosphorylethanolamine, and this diester was a competitive inhibitor of GPC hydrolysis.4. The GPC-splitting activity of such extracts was maximal at pH 7-5 and was stimulated by the addition of Mg2+ (10-S M).Similar concentrations of Mn2+ and Ca2+ were inhibitory and this also applied to higher concentrations of Mg2+.5. The enzyme was not sensitive to fluoride, iodoacetate, eserine or dii8opropylphosphorofluoridate.However, ethylenediaminetetraacetic acid and Zn2+ were strong inhibitors.6. Evidence has been obtained for the presence of the enzyme in other tissues of the rat, but it is virtually absent from the liver of the sheep.Activity was not observed in rat plasma, but it was found in the blood corpuscles.