The Influence of Divalent Cations and Substrate Concentration on the Incorporation of Myo‐inositol into Phospholipids of Isolated Bovine Oligodendrocytes

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Abstract
The incorporation of myo-inositol into phosphatidylinositol by 2 routes (CTP-dependent and CTP-independent) was investigated in homogenates prepared from isolated bovine oligodendrocyte perikarya. The CTP-dependent route has the higher maximum velocity of inositol incorporation and can utilize either Mn2+ or Mg2+ as a divalent ion cofactor. This route of inositol incorporation is also strongly inhibited by Ca2+ ions at concentrations less than 1 mM. The primary site of the inhibitory action appears to be the enzyme CDP-diglyceride inositol phosphatidyl transferase (EC 2.7.8.11) though synthesis of CDP-diacylglycerol is also inhibited by endogenous Ca2+ present in the oligodendrocyte homogenate. CTP-independent inositol incorporation into phosphatidylinositol is only stimulated by Mn2+ (Zn2+, Cu2+, Mg2+, Ca2+ and Co2+ are ineffective) and is not inhibited by Ca2+, at least up to a concentration of 1 mM.