Phosphomannose Isomerase

Jephcott and Robison (1) isolated mannose-6-phosphate as a product of fermentation of mannose by dried yeast.They observed a greater accumulation of this ester at 38" than at 20" and suggested that the isomerization of mannose-6-phosphate was inhibited at the higher temperature.The occurrence of isomerization in the fermentation of mannose was indicated by the observation of Young (2) that the three fermentable hexoses formed the same hexose diphosphate when incubated with yeast juice and With inorganic phosphate.An isomerase which catalyzes the equilibrium between glucose-6-and fructoseB-phosphate was first demonstrated by Lohmann (3) with extracts prepared from yeast, muscle, and other mammalian tissues.Somers and Cosby (4) found a similar enzyme in pea meal.It seems clear that this enzyme is widely distributed in nature.The existence of a separate phosphomannose isomerase has been reported (5).The present paper is concerned with the partial purification of this enzyme from extracts of rabbit muscle and the equilibrium catalyzed by it. Materials and MethodsMannose-B-phosphate was prepared by the action of adenosinetriphosphate (ATP) on mannose (Pfanstiehl's c.p. special quality) in the presence of crystalline yeast hexokinase (6).Glucose-6-phosphate, prepared from potato starch (7), was kindly supplied by Dr. T. Posternak.Fructose-6-phosphate was prepared from calcium fructose-l ,6-diphosphate (Schwarz Laboratories) by a modification of the method of Neuberg et al. ( 8).The monophosphate was kindly furnished by Dr. J. F. Taylor.Triphosphopyridine nucleotide (TPN) was prepared, in collaboration with Dr. D.