CIRCULAR DICHROISM OF JAPANESE-RADISH PEROXIDASE A

Circular dichroic (CD***) spectra of Japanese-radish peroxidase a (JRP-a***) [EC 1.11.1.7] and its derivatives were measured over the wavelength range of 202 to 700 mμ, and the results were compared with those of the synthetic polypeptides with well-established conformations. CD spectra in the far ultraviolet region indicated the presence of α-helical structure in the native JRP-a and some of its derivatives at neutral and alkaline pH. Acidification of JRP-a solution destroyed the helical structure, and a CD spectrum characteristic of the β-structure was obtained. Apo-JRP-a exhibited only the presence of the β-structure even at neutral pH. In the aromatic region, the fine structures were observed, some of which were consistent with those of the absorption curves. The fact that the, fine structure appeared in apo-JRP-a indicated that it should be assigned to the aromatic amino acids but not to the heme chromophore. The Soret and visible CD spectra of JRP-a and its alkaline, reduced, fluoride and cyanide derivatives were also measured, and some of the origins of the transitions in the heme chromophore were discussed. © 1969 BY THE JOURNAL OF BIOCHEMISTRY.