Semisynthetic Enzymes: Characterization of Isomeric Flavopapains with Widely Different Catalytic Efficiencies

Article abstract of DOI:10.1021/ja00334a053

Flavopapain 6 has been prepared by alkylation of the active site cysteine-25 of papain with 8α-(bromoacetyl)-10-methylisoalloxazine.This semisynthetic enzyme was shown to serve as a catalyst for the oxidation of dihydronicotinamides, exhibiting saturation kinetics and up to 600-fold rate accelerations relative to a model flavin.This is contrasted to the behavior of flavopapain 9, the product of the modification of papain with 6α-(bromoacetyl)-10-methylisoalloxazine.In this case no catalytic rate enhancement compared to the behavior of a model compound is observed.Since the two isoalloxazines are isomeric, the differences in the activities of the semisynthetic enzymes are interpreted in terms of differences in the geometry of the flavin at the active site.It is also noted that flavopapain 6 can exhibit some chiral discrimination toward optically active dihydronicotinamides.