Studies on the biosynthesis of cyclitols, XXXVII. On mechanism and function of Schiff's base formation as an intermediary reaction step of myo-inositol-1-phosphate synthase from rat testicles.

It could be shown that the formation of a Schiff's base by myo-inositol-1-phosphate synthase of rat testicles occurs by binding the aldehyde group of the open form of its substrate, D-glucose 6-phosphate, to a lysyl residue of one or both smaller subunits of the enzyme. The participation of the Schiff's base formation in the catalytic process is supported by the observations that (a) no Schiff's base is formed if NAD is removed from the enzyme, and (b) in the presence of NAD, the dehydrogenation step involved in the catalytic mechanism apparently takes place rapidly after the formation of the Schiff's base.