Photooxidation of Hog Pancreatic a Amylase

The findings suggest that histidine is present at the "active site " of hog pancreatic a amylase. The functions of a and P amylase are explained. Comparison of the "active sites " of a and ( amylase offers an opportunity to assess the hypothesis that enzymes functioning by an identical mechanism, at a common re-action site, but with opposite stereochem-istry, have identical amino acids involved in catalysis. Thoma, Wakim, and StewartL compared the active sites of a and ( amy-lase. Their data supported the hypothesis of Koshland, Ray, and Erwin2 that there might be a similarity between the active sites of enzymes catalyzing similar reac-tions, and also suggested that an imidazole and carboxyl group were at the active site of hog pancreatic a amylase. Studies of pH dependence indicated that groups with pKa of 4.6 and 6.7 were required for a amylase activity. Thoma, Wakim, and Stewart' were able to show that neither tyrosyl, phosphate, or N-terminal amino groups were associated with the pKa 6.7 depen-dent group. McGeachin and Brown3 showed that N-terminal a amino groups were more important to a amylase activity than internal a or E amino groups. The same conclusion was reached by acetylation of the enzyme with acetic anhydride.4 Thoma and Koshland5 showed that his-tidine, methionine, and carboxyl residues were at the active site of ( amylase. Cald-well, Weill, and Weil6 showed that fre