A qualitative study of the melanins from blue and brown human eyes

Abstract

This investigation compares the physical and chemical properties of melanins isolated from the human Eye Bank eyes which were divided into two groups viz. blue and brown on the basis of the colour of the iris. The uveal tissues in each group were pooled and homogenized with water. The supernatants after removal of debris were mixed with equal volumes of 12 n-HCl. The mixture was refluxed for 48 hr. The protein-free melanin was washed with water and dried. The melanin from blue eyes had a bluish tinge and that from brown eyes was brown. There was no significant difference between the U.V.-vis spectra of the two melanins. The i.r. spectra showed a characteristic major band in the region of 1000/cm which was absent in dopa melanin. Both blue and brown eye melanins showed similar composition of C,H,N and S. Protoporphyrin, chlorpromazine and paraquat formed complexes with these melanins. Both melanins catalyzed a few oxidation-reduction reactions. No significant difference in their catalytic activity in the coupled oxidation of NADH and reduction of ferricyanide was observed. However, the brown melanin-protoporphyrin complex showed decreased activity in the oxidation-reduction reaction as compared with blue melanin complex. Our studies show that although they are similar in most respects there are some differences in the physical and chemical properties of melanins from the blue and brown eyes.