SPECTROSCOPIC STUDY OF THE TEMPERATURE-DEPENDENT CONFORMATION OF GLUCOAMYLASE

Vibrational circular dichroism, electronic circular dichroism and infr ared absorption with Fourier self-deconvolution have been used for a c onformational 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 rel atively constant to 50 degrees C and then sharply decreases by a facto r of more than three by 60 degrees C. This decrease in helix is primar ily compensated by a rise in the fraction of beta-sheet; but bend, tur n and 'other' components also increase. By comparison of the three tec hniques, it was determined that the electronic CD analysis was quantit atively in error due to interference by glycosidic residues. The inher ent resolution of the vibrational techniques, FTIR and VCD, avoids suc h interference.