Spectroscopic study of the temperature-dependent conformation of glucoamylase.

Vibrational circular dichroism, electronic circular dichroism and infrared absorption with Fourier self-deconvolution have been used for a conformational study of the small form, G2, of glucoamylase, 1,4-alpha-D-glucan glucohydrolase from Aspergillus niger (EC 3.2.1.3) in aqueous solution. From the temperature dependence of spectra measured from 25 degrees C to 60 degrees C it was seen that the helical content is relatively constant to 50 degrees C and then sharply decreases by a factor of more than three by 60 degrees C. This decrease in helix is primarily compensated by a rise in the fraction of beta-sheet; but bend, turn and 'other' components also increase. By comparison of the three techniques, it was determined that the electronic CD analysis was quantitatively in error due to interference by glycosidic residues. The inherent resolution of the vibrational techniques, FTIR and VCD, avoids such interference.