Studies on chemiluminescence in the enzymatic and autoxidative transformation of 3,4-dihydroxyphenylalanine into eumelanins.

The catechol oxidase-catalysed and autoxidative transformation of 3,4-dihydroxyphenylalanine (DOPA) to eumelanin have been studied by oxygen consumption, energy transfer, absorption and fluorescence spectroscopy. Formation of transient dopachrome (lambda max = 480 nm) and dopalutin (lambda ex = 423 nm, lambda em = 491 nm) have been found in the enzymatic and autoxidative reaction. In the enzymatic reaction, neither a photon emission with quantum yield phi greater than 10(-13) nor energy transfer to triplet and singlet energy acceptors (sensitizers such as anthracene derivatives, xanthene dyes and chlorophyll-a) in water and micellar solutions have been found. The autoxidative reaction is chemiluminescent (phi = 10(-9)), the emission occurring in the 400-600 nm range. The excitation energy is not transferred to sensitizers. The effect of various enzymes and traps of active oxygen species as well as the spectral distribution of chemiluminescence indicate that there is no emission from oxygen dimoles. Carbonates and active species of oxygen are shown to participate in the chemiexcitation reaction.