Faculty Collaboration Database

Interactions of flavins with melanin. Studies on equilibrium binding of riboflavin to dopa-melanin and some spectroscopic characteristics of flavin-melanin complex. Biophys Chem 1990 Oct;38(1-2):39-48

Date

10/01/1990

Pubmed ID

2128193

DOI

10.1016/0301-4622(90)80038-9

Scopus ID

2-s2.0-0025076830 (requires institutional sign-in at Scopus site)   15 Citations

Abstract

Natural melanins are photoprotective pigments that in mammals are principally found in the skin, hair, and eyes. Although the molecular mechanism of photoprotection of pigmented cells has not yet been established, several hypotheses have been proposed with melanin acting as a light filter, free radical scavenger, and quencher of electronically excited states of reactive intermediates. It can be expected that the detoxicating efficiency of melanin should be enhanced if the melanin and potentially cytotoxic species are brought close together. Such a situation may occur for a number of photosensitizing dyes that have the ability to bind to melanin. The interaction of melanin with flavins has been studied under strictly controlled experimental conditions. The equilibrium dialysis method has been employed to determine dissociation constants and the number of binding sites in melanin at pH 5-9. The data reveal that synthetic DOPA-melanin has two different classes of binding sites with dissociation constants of 10(-6) and 10(-5) M, respectively. The overall binding capacity of melanin, at pH 7, is 250 nmol RF/mg melanin. The amount of bound-to-melanin RF increases with pH. The absorption spectra of melanin complexes with RF and lumiflavin indicate that hydrophobic interaction may be involved in the binding of these flavins by melanin. No changes in flavin fluorescence have been detected after binding of flavin to melanin. It appears that, contrary to cationic photosensitizing dyes, the singlet excited state of flavin molecules is not quenched by melanin.

Author List

Kozik A, Korytowski W, Sarna T, Bloom AS

Author

Alan Bloom PhD, MA Emeritus Professor in the Pharmacology and Toxicology department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Binding Sites
Dihydroxyphenylalanine
Hydrogen-Ion Concentration
Kinetics
Photochemistry
Riboflavin
Spectrometry, Fluorescence
Spectrophotometry, Ultraviolet