Circular dichroism of turnip peroxidases

Circular dichroic (CD) spectra of two turnip isoperoxidases, P1 and P7, and of their derivatives were measured over the wavelength range of 200 to 650 nm. For the two isoenzymes, it was observed that although the visible and Soret bands are located at similar wavelengths, their ellipticities are different. These results suggest that the active sites are similar but that differences do exist. The results are compared with those reported for Japanese radish peroxidase a and horseradish peroxidase. It appears that a common property of plant peroxidases is the presence of negative CD Soret bands for the reduced forms and their inversion upon cyanide binding. The CD spectra in the far UV region indicate an appreciable helical content for both native enzymes and their various derivatives. The calculated contents of unordered structure are very high (greater than 50% for either P1 or P7), in agreement with other studies on glycoproteins.