In our experiments Fe(III) was used as a YM155 supplier nutrient since we used ferric ammonium citrate as the medium substrate. Fungal melanins are able to reduce Fe(III) to Fe(II), and this oxidative change prevents the formation of oxidative radicals when iron reacts with hydrogen peroxide, thus protecting the fungus from oxidative stress [28].
Cunha et al. [12] demonstrated that untreated F. pedrosoi has more abundant and homogeneous binding to cationised ferritin (a Fe(III) complex) on the cell wall surface than fungi treated with TC. At the time, the stronger binding was attributed to more anionic groups on the surface of the control and melanin’s affinity to iron. Experiments with melanin from C. neoformans [28] suggests that it acts as a redox buffer, changing its oxidative state according to the chemical stimuli in its EVP4593 clinical trial environment. Thus, it is possible that melanin maximises its PRI-724 order antioxidant potential by reducing Fe(III) to Fe(II), ensuring the balance of its redox chemical microenvironment and minimising the effect of oxidation of fundamental structures on fungal growth. The novel findings of this work led us to propose
that the melanin of F. pedrosoi reacts with ferric iron to reduce it to ferrous iron, and maintains this iron-melanin complex as a redox buffer to trap oxidative radicals. This explains the higher growth rate of the control F. pedrosoi samples compared to the TC-treated samples following exposure to NO and hydrogen peroxide (Fig. 4), as well as the higher susceptibility of the TC-treated samples to activated macrophages [12]. The progressive microwave power saturation ESR
experiments, which varied the power of the microwaves on the magnetised sample, showed approximately a two times higher intensity in the control-melanin PtdIns(3,4)P2 samples compared to the TC-melanin samples. According to our hypothesis, this suggests that control-melanin has more self-interaction sites as well as interaction sites for associated structures and therefore is more compact. As indicated by Herbst et al. [29], the profile of progressive microwave power saturation curves of amorphous solids is linked to the effectiveness of spin relaxation pathways for the paramagnetic centre that interacts with its surroundings. Hence, the measure of the progressive microwave power saturation curves for similar paramagnetic centres may provide an indirect indication of molecular arrangements. In this study, the profiles observed for control-melanin (Fig. 1) suggest that it is a more compact polymer than TC-melanin because its spin relaxation rates are faster. Such data are in agreement with the thinner cell wall of untreated F. pedrosoi conidia compared to TC-treated F. pedrosoi as revealed by freeze-fracture assays [30]. Our data from interaction assays between fungi and activated murine macrophages suggest that melanin is involved in the protection of the fungus against NO.