CIRCULAR-DICHROISM AND FOURIER-TRANSFORM INFRARED SPECTROSCOPIC STUDIES ON THE SECONDARY STRUCTURE OF SACCHAROMYCES-CEREVISIAE AND ESCHERICHIA-COLI PHOSPHOENOLPYRUVATE CARBOXYKINASES

The secondary structure of Saccharomyces cerevisiae and Escherichia co li phosphoenolpyruvate (PEP) carboxykinases was quantitatively examine d using circular dichroism (CD) and Fourier transform infrared (FTIR) spectroscopies. From CD analyses, values of 24% alpha-helix and 38% be ta-sheet were obtained for the E. coli enzyme, while the corresponding values for the S. cerevisiae PEP carboxykinase were 20% and 36%. Anal ysis of the amide I' infrared band indicated 20% alpha-helix and 36% b eta-sheet for the S. cerevisiae enzyme, while for the E. coli protein values of 40% beta-sheet and between 9 and 36% alpha-helix could be in ferred. It is concluded that the bacterial enzyme has more secondary s tructure elements than the yeast protein. No alteration of the CD or F TIR spectra was detected upon substrate or metal ion binding to any en zyme.