The present state of our knowledge about the biosynthetic processes leading to the inositols is reviewed. On the basis of experimental data obtained in the laboratory of the authors and by other groups working on the problem, anew mechanism of action for the mammalian myo-inositol- 1-phosphate synthase is suggested. The central position of myo-inositol in the synthesis of the other inositols is described.

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Enzyme preparations from oat seedlings showing the activity of myo-inositol oxygenase (E.C.1.13.99.1) have been described previously. In contrast to myo-inositol oxygenase preparations from other sources, e.g. rat kidney or yeast, the oat enzyme seemed to exhibit a somewhat less stringent activity, acting on other inositols and inositol methyl ethers as well as on myo-inositol. By purification of the enzyme present in the extract from oat seedlings with the help of an affinity gel specific for enzymes acting on myo-inositol a homogeneous enzyme preparation was obtained, which shows the same strict specificity as the myo-inositol oxygenase from other sources. It has a molecular weight of 62,000 and tends to aggregate to oligomers (up to tetramers) under physiological pH-values; in more alkaline media dissociation to monomers is observed. The action on the other inositols and inositol methyl ethers is apparently due to one or more other enzymes, which are also adsorbed on the affinity gel, but can be separated from the myo-inositol oxygenase by elution with increasing concentrations of myo-inositol.