Glucosidase substrate analog inhibitor

In order to account for the inability of many enzymes to bind the protonated form of the basic inhibitors or permanently cationic ones better than uncharged analogs (for example, yS-o-galactosidase from E. coli, and P-v>-glucosidase from almonds), it was proposed that the enzyme could proton-ate the inhibitor at the active site by a cationic acid (for example, protonated histidine). If proton transfer cannot occur, the attractive forces due to the carboxylate would be canceled by the repulsion from the cationic acid. Experimental evidence for this proposal is, however, still lacking. In fi-D-gn-lactosidase from E. coli, a tyrosine is presumed to be responsible for the protonation of substrates. ... 

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