Myoinosose-2 1-phosphate: an intermediate in the myoinositol 1-phosphate synthase reaction.

Partially purified testicular myoinositol 1-phosphate synthase was incubated with glucose 6-phosphate and NAD+. After 2 min the reaction was stopped by the addition of NaB3H4. Phosphorylated reduced sugars were isolated by ion exchange and dephosphorylated enzymatically. Scylloinositol and myoinositol, added as carriers, were re-isolated and purified to constant specific radioactivity. Since scylloinositol phosphate is uniquely related to myoinosose-2 1-phosphate, the finding of labeled scylloinositol and myoinositol is considered strong evidence for the presence of myoinosose-2 1-phosphate, an intermediate which has been postulated in the synthase-catalyzed isomerization of glucose 6-phosphate to myoinositol 1-phosphate. About one-half the amount of intermediate was demonstrable with boiled synthase, indicating firm binding of myoinosose-2 phosphate to the enzyme.