Cooperativity of papain-substrate interaction energies in the S2 to S2' subsites.

Enzyme-substrate contacts in the hydrolysis of ester substrates by the cysteine protease papain were investigated by systematically altering backbone hydrogen-bonding and side-chain hydrophobic contacts in the substrate and determining each substrate's kinetic constants. The observed specificity energies [defined as delta delta G obs = -RT ln [(kcat/KM)first/(kcat/KM)second)]] of the substrate backbone hydrogen bonds were -2.7 kcal/mol for the …