Raman studies of the conformation of the basic pancreatic trypsin inhibitor

The vibrational Raman spectra of the basic pancreatic trypsin inhibitor in aqueous solution, as lyophilized powder and in a single crystal and presented. The thermal stability of this protein is demonstrated by the fact that minor alterations in the spectrum, mainly in the amide III band near 1260 cm-1, occur in the solution spectrum only at temperatures above 75 degrees C. No significant spectral changes appear when the pH value of the solution is varied in the range from 1.5 to 8.7. The distinct differences of the powder spectrum compared to that of the solution, show that lyophilization causes appreciable conformational changes both in the main-chain and in the side-chains. A difference in main chain conformation of the basic pancreatic trypsin inhibitor in single crystal and in solution is suggested by different amide III frequencies.