Ultraweak photon emission in model reactions of the in vitro formation of eumelanins and pheomelanins.

Ultraweak luminescence in the spectral region 300-660 nm is generated in the enzymatic (tyrosinase EC.1.14.18.1) and autooxidative polymerization of L-DOPA, 5-S-cysteinyl-DOPA, and L-DOPA + cysteine to eumelanins and pheomelanins, respectively. Using sensitive calibrated single photon counting equipment, the photon emission intensity I and quantum yield phi have been measured: I = 10-100 h nu/s cm3, phi less than or equal to 10(-13) for enzymatic reactions, and I = 500-3000 h nu/s cm3, phi greater than or equal to 5 x 10(-12) for autooxidative ones. 5-S-cysteinyl-DOPA and cysteine exhibit diminished I and phi-values relative to DOPA. Tests with chemiluminogenic probes-luminol and lucigenin, SOD, catalase, peroxidase, H2O2, and spectrophotometric measurements indicate that photon emission is associated with degradative oxidations of melanin subunits by means of active oxygen species as H2O2 and O2.