|
In order to obtain a clue in understanding enzymatic hydrolysis in which the His-Cys moieties of papain protease is involved, we prepared cationic peptide-sufactants bearing histidyl, cysteinyl, and both histydyl and cysteinyl residues. Their catalytic efficiency toward the hydrolysis of PNPL were investigated in comicellar phases formed with N+C2CysC12, N+C2HisC12, N+C2HisCysC12 increased markedly in the same order compared with that of N+C2AlaC12. The markedly increased catalytic effects are attributed to the imidazole groups of N+C2HisC12 and the thiol groups of N+C2CysC12, and the large catalytic efficiency of N+C2HisCysC12, is considered due to the interaction of the imidazole and the thiol groups. In order to investigate catalytic activities, rate constants for the functional groups, km* and dissociation constants, pKa have been determined. The results showed that km* and pKa of the imidazole groups were 7.91 × l0-4 S-1 and 6.49, and those of the thiol groups were 6.00 × 10-4S-1 and 10.50. The catalytic effects of comicellar systems on the hydrolysis of p-nitrophenyl esters has increased according to the increasing size of the alkyl carbon number. Therefore, the catalytic effects have been increasing by the interaction of micellar hydrophobic parts and substrates as well as action of the functional groups.
|