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Pyomelanin mimics from homogentisic acid (HGA) and gentisic acid (GA) were biosynthesized by the oxidative enzyme T. versicolor laccase at physiological pH to obtain water soluble melanins. The pigments show brown-black color, broad band visible light absorption, a persistent paramagnetism and high antioxidant activity. The EPR approach shows that at least two different radical species are present in both cases, contributing to the paramagnetism of the samples. This achievement can also shed light on the composition of the ochronotic pigment in the Alkaptonuria disease. On the other hand, these soluble pyomelanin mimics, sharing physico-chemical properties with eumelanin, can represent a suitable alternative to replace the insoluble melanin pigment in biotechnological applications.

An actinobacteria strain was isolated from Algerian Sahara soil and assigned to Streptomyces cyaneofuscatus Pridham et al. 1958 species. This strain was selected for its ability to produce melanin exopigments in liquid and solid media. Melanin synthesis was associated with tyrosinase activity and the enzyme from this strain was isolated and biochemically characterized. Synthetic melanin was then enzymatically produced using the S. cyaneofuscatus Pridham et al. 1958 tyrosinase. As this enzyme showed a higher diphenolase activity, a synthetic melanin from the enzymic oxidation of 3,4-dihydroxyphenylalanine (dopa) was obtained by the use of a Trametes versicolor (L.) Lloyd laccase for comparison. The natural and synthetic pigments were physico-chemically characterized by the use of ultraviolet (UV)-Visible, and Fourier transform infrared (FT-IR) and multifrequency electron paramagnetic resonance (EPR) spectroscopies. All the melanin samples displayed a stable free radical when analyzed by X-band EPR spectroscopy. Once the samples were recorded at Q-band EPR, a copolymer derived from a mixture of different constituents was evident in the natural melanin. All radical species were analyzed and discussed. The use of water-soluble melanin naturally produced by S. cyaneofuscatus Pridham et al. 1958 represents a new biotechnological alternative to commercial insoluble pigments.

An actinobacteria strain was isolated from Algerian Sahara soil and assigned to Streptomyces cyaneofuscatus Pridham et al. 1958 species. This strain was selected for its ability to produce melanin exopigments in liquid and solid media. Melanin synthesis was associated with tyrosinase activity and the enzyme from this strain was isolated and biochemically characterized. Synthetic melanin was then enzymatically produced using the S. cyaneofuscatus Pridham et al. 1958 tyrosinase. As this enzyme showed a higher diphenolase activity, a synthetic melanin from the enzymic oxidation of 3,4-dihydroxyphenylalanine (dopa) was obtained by the use of a Trametes versicolor (L.) Lloyd laccase for comparison. The natural and synthetic pigments were physico-chemically characterized by the use of ultraviolet (UV)-Visible, and Fourier transform infrared (FT-IR) and multifrequency electron paramagnetic resonance (EPR) spectroscopies. All the melanin samples displayed a stable free radical when analyzed by X-band EPR spectroscopy. Once the samples were recorded at Q-band EPR, a copolymer derived from a mixture of different constituents was evident in the natural melanin. All radical species were analyzed and discussed. The use of water-soluble melanin naturally produced by S. cyaneofuscatus Pridham et al. 1958 represents a new biotechnological alternative to commercial insoluble pigments.