Purification, structure and anti-radiation activity of melanin from Lachnum YM404.

Extracellular melanins (LEM404) were extracted from Lachnum YM404 with a yield of 3.45 g/L. LEM404-a, LEM404-b, LEM404-c, LEM404-d and LEM404-e were fractionated from LEM404 by Sephadex G-15 column. LE404-a was detected as the homogeneous component with molecular weight of about 432.18 Da. Based on the elemental analysis, mass spectrometry, infrared spectroscopy, pyrolysis-GC-MS and NMR analysis, the molecular formula (C22H12N2O4S2) and structural formula of LEM404-a were concluded. LEM404-a could significantly increase the survival rates of Escherichia coli, Staphylococcus aureus and Saccharomyces cerevisiae under UV radiation. Anti-radiation experiments in mice showed that the skin manifestations in mice of low radiation dose experimental group (LEG) were similar to those in blank control group (BCG). Compared with the control groups (LCG and HCG), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities in mice of experiment groups (LEG and HEG) were improved significantly while malondialdehyde (MDA) content were decreased significantly, indicating that LEM404-a had strong anti-ultraviolet radiation activity.

Physicochemical characteristics and antioxidant activity of arginine-modified melanin from Lachnum YM-346.

Seven kinds of amino acids were used to modify the non-water-soluble extracellular melanin (LEM346) from Lachnum YM-346. It was found that arginine-melanin (ALEM346) had the highest solubility, being 4.55% (gg(-1)) in 30°C distilled water. Elemental analysis, infrared spectrum and mass spectrum analysis revealed that LEM346 molecule contained indole quinone structure, its molecular formula speculated to be C(18)H(8)O(6)N(2). Infrared spectrum analysis showed that ALEM346 had characteristic absorption peaks at 1672.346 and 1637.679 cm(-1). Mass spectrum analysis indicated that ALEM346 contained three types of arginine-melanin molecules. When the ALEM346 concentration was 500 mgL(-1), its total antioxidant capacity was equivalent to α-tocopherol of 46.65 mmolL(-1), the DPPH() and O(2)(-) scavenging rates and the Fe(2+) chelating rate were 89.05%, 93.81% and 80.18%, respectively, suggesting that the antioxidant activity of ALEM346 was stronger than that of LEM346.