On the mechanism of action of phosphoglucose isomerase and phosphomannose isomerase.

This transformation is intramolecular and would involve no exchange between the migratory hydrogen and hydrogen in the aqueous solvent. (2) The hydrogen may migrate as a proton (Fig. l), in which case exchange with the solvent would occur. In order to distinguish between these alternatives the conversion of fructose-6-phosphate (F-6-P) into glucose-6phosphate (G-6-P)) catalyzed by phosphoglucose isomerase, was conducted in the presence of deuterium oxide. With respect to possible products derivable from a given aldose, while it is conceivable that both a ketose and a second aldose might be formed, it becomes more and more apparent (l-5) that in isomerization reactions of this type there is not a direct conversion of one aldose into the corresponding diastereoisomeric aldehyde; instead, the corresponding ketose is first formed which can then, in some cases, give rise to the second aldehyde. Some of the mechanistic reasons for these relationships have been investigated.