Isolation of Crystalline Phosphoglucose Isomerase from Brewers' Yeast.

In a program to elucidate the mechanism by which phosphoglucose isomerasel participates in the catalyzed isomerization between glucose 6-phosphate and fructose g-phosphate, isolation of the enzyme from several sources is pursued as the basis for quantitative studies of its protein nature. The comparative investigation of several heteroenzymes appears to be a valuable tool in identifying the structure of an enzyme at and around the active site since it will provide clues as to catalytically important features of the protein molecule. Phosphoglucose isomerase has been previously isolated in this laboratory in crystalline form from rabbit skeletal muscle (2), and from bovine skeletal muscle .* Earlier attempts at isolation of phosphoglucose isomerase from brewers’ yeast (3) had met with only partial success when a highly purified but still amorphous enzyme preparation was obtained. This communication now reports the isolation in crystalline form of phosphoglucose isomerase from brewers’ yeast (Sacchuromyces carlsbergensis). It will be of interest also to include in these comparative studies the crystalline enzyme from bakers’ yeast; thus far however, the isolation procedure for this enzyme has only appeared in the form of a short note (4).