Effect of nucleotides on the incorporation of myo-inositol into phosphatidylinositol in rat liver microsomes.

In rat liver microsomes the incorporation of inositol in the presence of Mn2+ was stimulated by cytidine nucleotides, whereas it was inhibited by other nucleotides. At low concentrations of CMP, AMP and other nucleotides stimulated inositol incorporation. No such effect was observed when the concentration of CMP was 2 mM or higher. It was found that an appreciable hydrolysis of CMP to cytidine and inorganic phosphate occurred during incubation with microsomes in the presence of Mg2+ or Mn2+. AMP was hydrolysed at a comparable rate. The activatory effect of AMP and other nucleotides on the CMP-dependent incorporation of inositol could be ascribed to protecting CMP against hydrolysis.