The enzymatic synthesis of inositol phosphatide.

Since the isolation of myo-inositol from biological sources over a hundred years ago, little has been reported concerning its metabolism. Experiments in nutrition have implicated inositol variously as a vitamin (1) and as a lipotropic agent (2) ; and more recently inositol has been identified as a soluble factor required for the survival of human cells grown in tissue culture (3). The presence of inositol lipides in mammalian tissue in the form of diphosphoinositide (4) and monophosphoinositide (inositol phosphatide) (5) has been established. Recently, several investigators have confirmed the observation that the exchange of inorganic P32 with the phospholipides of tissue slices and homogenates occurs at a greater rate in the inositol lipide fraction than in the ethanolamine-, choline-, or serine-containing fractions (69). In the present study, the metabolism of inositol was investigated by means of a spectrophotometric method for the determination of inositol and by the use of tritium-labeled inositol. A particulate preparation obtained from lyophilized guinea pig kidney mitochondria which catalyzed the incorporation of inositol into inositol phosphatide in the presence of cytidine nucleotide and Mg++ was examined in detail.