Homogentisic Acid and Gentisic Acid Biosynthesized Pyomelanin Mimics: Structural Characterization and Antioxidant Activity

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.

Automated summary

In this study, water soluble melanins were successfully biosynthesized from homogentisic acid and gentisic acid by the oxidative enzyme T. versicolor laccase at physiological pH. The melanins showed high antioxidant activity, persistent paramagnetism, and broad band visible light absorption. EPR analysis revealed the presence of at least two different radical species in each case, contributing to the paramagnetism observed in the samples. This achievement may have implications for understanding the composition of the ochronotic pigment in Alkaptonuria disease, and the soluble pyomelanin mimics could serve as a viable alternative to replace insoluble melanin pigment in biotechnological applications.