Structure and reactivity of aerosol-OT reversed micelles containing α-chymotrypsin

Abstract

The structure and reactivity of α-chymotrypsin solubilized in biological buffer–sodium bis(2-ethylhexyl)sulfosuccinate (AOT)–2,2,4-trimethylpentane (isooctane) reversed micelles, have been studied at various water/surfactant molar ratios (ω_o) and protein concentrations using synchrotron radiation X-ray small-angle scattering and enzymatic activity measurements. Two types of α-chymotrypsins and two different substrates (p-nitrophenyl acetate and p-nitrophenyl caprylate) were used. The scattering experiments show that α-chymotrypsins are entrapped in the water pools. In the low ω_o range (0 < ω_o < 12) oligomeric AOT reversed micellar formation occurs as a metastable state and simultaneously the enzymatic activity is enhanced significantly for both types of α-chymotrypsins, showing a maximum activity at ω_o≈ 12 for both substrates. The results from the scattering and enzymatic activity measurements suggest that the hydrolysis of the above esters, catalysed by α-chymotrypsins, is enhanced at the internal interface of the AOT reversed micelle and that the metastable oligomeric phase plays an important role in accelerating the metabolic turnover by increasing the apparent interfacial area of the micelles close to the enzymes.