A new low-molecular-weight peptide with phenol oxidase activity, named Pc factor, was isolated; purified from liquid culture of a white-rot basidiomycete Phanerochaete chrysosporium. Its molecular weight was about 600 Da estimated by gel-filtration. Three amino acids Glu, Gly; Val were detected in hydrolysate. Absorption peaks corresponding to amino acids; peptide were observed by UV; IR spectra analysis. And the signal of Cα of amino acid was also detected by [13]C-NMR method. Pc factor had high thermostability; remained active in weakly alkalescent pH range. It could chelate Fe[3+]; reduce it to Fe[2+], but no hydroxyl radical HO˙ could be detected during the reaction process. It could oxidize phenolic lignin-model compounds such as 2,6-dimethoxyphenol (2,6-DMP), 2,2′-azinobis (3-ethylbenzathiazoline-6-sulfinic acid) (ABTS); syringaldazine in the absence of Mn[2+]; H2O2. These characteristics differed greatly from those of manganese peroxidases. The oxidative catalysis of Pc factor can be enhanced by certain metal ions such as Cu[2+]; Mn[2+] etc.,; O2 molecule was necessary for this reaction. In summary, Pc factor may function as an electron carrier in this novel oxidation-reduction system.
Among 27 filamentous fungi, a strain Aspergillus niger An76 gave the highest siderophore yield even when cultured on natural medium or minimal medium containing 1 mmol L^-1 Fe^3＋. Whereas for most other strains, the capacities of siderophore production was repressed as the concentrations of Fe^3＋ was higher than 20 ~tmol L^-1. Lower ferric iron concentrations were more conducive to siderophore synthesis for those strains. The An76 siderophore was partially purified through a series of chromatography steps using Sephadex LH20 and CM-Sepharose Fast Flow columns. Its structural characteristics differed from typical siderophores, such as catecholates or hydroxamates, and no amino acids or peptide bonds were detected. It may therefore represent a new type of siderophore structure. TBA assay and ESR trapping studies showed that An76 siderophore had remarkable scavenging activity of hydroxyl free radicals in vitro. The antibiotic activities of siderophores produced by An76 were tested against 29 bacterial strains, including plant, animal, and human pathogens. The growth of 14 bacterial strains could be completely inhibited at a siderophore concentration of 8 mg ml^-1 with an incubation time of 30 min. Evidence suggests that the An76 siderophore has potential value as an antioxidant and a biocontrol agent against pathogenic microorganisms.
