CARBOXYPEPTIDASE-Y CATALYSIS IN TERNARY-SYSTEMS CONTAINING OCTYL BETA-D-GLUCOPYRANOSIDE, OCTANOL, AND WATER

The hydrolysis and peptide formation reactions of carboxypeptidase Y ( CPDY) were studied in a ternary system consisting of octyl beta-D-gluc opyranoside (beta-OG), water, and octanol (OcOH). This was performed t o elucidate the effects of the structures of the surrounding medium on biocatalytic reactions, with special reference to enzyme reactivity a nd the morphology of the surfactant aggregates. First, the effect of b eta-OG on the catalytic activity of CPDY (hydrolytic reaction) was stu died in a surfactant/water binary system. beta-OG was found to inhibit CPDY activity for Suc-Ala-Ala-Pro-Phe-pNA, but somehow accelerated th e reaction with Bz-Tyr-pNA. When the CPDY reactions were measured unde r several conditions in the phase diagram of the ternary system, CPDY was found to be strongly affected by the size and form of the microstr uctures in each phase. In the reverse micelle (L(2)) phase, the hydrol ytic rate was maximally increased with an increase in the water conten t; the highest rate was observed at the boundary of the L(2)/2L or L(2 )/F (reversed cylindrical diameter) phase. In the aminolysis reaction catalyzed by this enzyme, a higher yield of the dipeptide was also obs erved near the boundary of the L(2)/2L or L(2)/D + X phase and also in the F phase. The fraction of aminolysis (f(a)) was relatively high an d rather insensitive to changes in the phase, with the exception that the f(a) was low in the D/X phase.