Ayako Nakazawa

Circular dichroism studies of complexes of sequential histidine polypeptides with methyl orange

Abstract The induced circular dichroism (c.d.) spectra of poly( l -histidine) and sequential histidine polypeptide-dye complexes were measured. Two dichroic bands associated with the blue shifted absorption shoulder of methyl orange at around 370 nm were observed by complex formation between the polypeptides and the dye. Induced c.d. arose from the dye bound to the polypeptide in random coil structure, the optimal pH being 4.1. Added sodium chloride decreases the intensity of the induced c.d. Intramolecular interaction was assumed from the relationship between the concentrations of the polypeptide-dye complex and the intensities of the induced c.d. The intensity of the induced c.d. decreases with increasing distance between the intramolecular histidine residues. The induced c.d. spectrum of the poly( l -histidine)-dye complex shows the irreversible thermal change when heating.