Multi-functional roles of a histidine residue in human pancreatic alpha-amylase

Functional roles of histidine residues at the active site in human pancreatic alpha-amylase were examined by protein engineering. Three histidine residues at 101, 201, and 299 were converted to asparagine residues, respectively. It was found that His201 played multi-functional roles concerning so many functions; substrate binding, control of optimum pH, change in substrate specificity, activation by chloride ion, and inhibition by a proteinaceous inhibitor.