Fourier transform infrared spectra studies of protein in reverse micelles: effect of AOT/isooctane on the secondary structure of α-chymotrypsin

The amide I region Fourier transform infrared (FTIR) spectra of alpha-chymotrypsin have been studied in deuterium oxide (D2O) solution and also in reverse micellar solution of AOT/isooctane. The Fourier second derivative was applied to all spectra, revealing that the amide I band of alpha-chymotrypsin in D2O and in reverse micellar solution consists of nine components. The band frequencies are assigned to alpha-helix, beta-sheet, random and turn structure. The second derivative spectra of alpha-chymotrypsin have been shifted in the reverse micellar solution of AOT/isooctane in comparison with its spectra in D2O. This shift has also changed the intensity of each band. Through accurate measurement of the band intensities, the relative amount of different structure of alpha-chymotrypsin can be estimated. The comparison of the calculated results obtained in D2O with those obtained in reverse micellar solution provides the possibility to analyze the effect of reverse micellar solution of AOT/isooctane on the secondary structure of alpha-chymotrypsin. The results indicate that the reverse micellar solution has decreased the amount of alpha-helix and beta-sheet structure and increased the amount of random and turn structure in alpha-chymotrypsin. The increase of the amount of random structure might loosen the structure of alpha-chymotrypsin and change the activity of the enzyme.