We investigated the mechanism of Coomassie brilliant blue G-250 (CBB) binding to proteins in order to develop a protein assay with the maximum possible sensitivity. We found that the neutral ionic species of CBB binds to proteins by a combination of hydrophobic interactions and heteropolar bonding with basic amino acids. On the basis of these findings, we developed a very sensitive hydrophobic assay for proteins (at the nanogram level) using the hydrophobic reagents ammonium sulfate and trichloroacetic acid under pH conditions that increase neutral species concentration in the assay reagent in order to enhance the binding of more CBB dye molecules per protein molecule than in previous CBB-based assays.

The combination of intense solar radiation and soil desiccation creates a short circuit in the biogeochemical carbon cycle, where soils release significant amounts of CO 2 and reactive nitrogen oxides by abiotic oxidation. Here we show that desert soils accumulate metal superoxides and peroxides at higher levels than non-desert soils. We also show the photogeneration of equimolar superoxide and hydroxyl radical in desiccated and aqueous soils, respectively, by a photo-induced electron transfer mechanism supported by their mineralogical composition. Reactivity of desert soils is further supported by the generation of hydroxyl radical via aqueous extracts in the dark. Our findings extend to desert soils the photogeneration of reactive oxygen species by certain mineral oxides and also explain previous studies on desert soil organic oxidant chemistry and microbiology. Similar processes driven by ultraviolet radiation may be operating in the surface soils on Mars.

cWe show here that oxidative stress is involved in both sclerotial differentiation (SD) and aflatoxin B1 biosynthesis in Aspergillus flavus. Specifically, we observed that (i) oxidative stress regulates SD, as implied by its inhibition by antioxidant modulators of reactive oxygen species and thiol redox state, and that (ii) aflatoxin B1 biosynthesis and SD are comodulated by oxidative stress. However, aflatoxin B1 biosynthesis is inhibited by lower stress levels compared to SD, as shown by comparison to undifferentiated A. flavus. These same oxidative stress levels also characterize a mutant A. flavus strain, lacking the global regulatory gene veA. This mutant is unable to produce sclerotia and aflatoxin B1. (iii) Further, we show that hydrogen peroxide is the main modulator of A. flavus SD, as shown by its inhibition by both an irreversible inhibitor of catalase activity and a mimetic of superoxide dismutase activity. On the other hand, aflatoxin B1 biosynthesis is controlled by a wider array of oxidative stress factors, such as lipid hydroperoxide, superoxide, and hydroxyl and thiyl radicals. Humans and animals are exposed to carcinogenic aflatoxins through contaminated food and feed, air, and drinking water (1, 2). Aspergillus flavus is the primary cause of aflatoxin-contaminated crops. A. flavus is a heterothallic fungus, and laboratory crosses produce ascospore-bearing ascocarps embedded within sclerotia. In the field, sclerotia are dispersed during crop harvest and require an additional incubation period on the soil for sexual reproduction (3). Despite the significant contribution of A. flavus to crop aflatoxin contamination, it is not yet known what the role of oxidative stress is for its sclerotial differentiation (SD) and aflatoxin B1 biosynthesis. Deciphering this relationship could contribute to the development of nontoxic antifungal means via the coinhibition of A. flavus SD and aflatoxin B1 biosynthesis.Several toxigenic and phytopathogenic fungi spread and survive in nature through the formation of conidiophores and resistant sclerotia. It has been known that oxidative stress regulates the sclerotial differentiation of filamentous phytopathogenic fungi such as Rhizoctonia solani, Sclerotium rolfsii, Sclerotinia sclerotiorum, and Sclerotinia minor (4, 5). Moreover, it has been established that the regulation of morphogenesis in aspergilli and other fungi is genetically linked to secondary metabolism (6-9). In A. flavus, both SD and aflatoxin biosynthesis are governed by the regulatory protein VeA (10). Deletion of the veA gene in this fungus results in the inhibition of sclerotia formation and aflatoxin biosynthesis (10). However, it is not known whether SD in A. flavus is regulated by oxidative stress and whether the deletion of veA could alter its oxidative stress levels.Previous reports have linked aflatoxin biosynthesis with oxidative stress in A. flavus and A. parasiticus both at the metabolic and transcriptional levels. Specifically, aflatoxin biosynthesis in both species is activated by high ...

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A simple protocol is presented for the assessment of superoxide radical in organisms (animal/plant tissues, microorganisms, cell cultures, biological/culture fluids) and soils, through the quantification of 2-hydroxyethidium (2-OH-E+), its specific reaction product with hydroethidine (HE). It is an alternative to the quantification of 2-OH-E+ by HPLC (restricted to cell cultures), offering the advantage of the in vivo assessment of superoxide radical in a wide range of experimental systems. The protocol includes alkaline-acetone extraction of the sample, purification by microcolumn cation exchange and hydrophobic chromatographies, and fluorescence detection of the isolated 2-OH-E+/HE-oxidation products mixture before and after consumption of 2-OH-E+ by a horseradish peroxidase/hydrogen peroxide system. The protocol is sensitive at <1 pmol 2-OH-E+ per mg protein (extended to the femto level when using large samples) in biological systems, and in soils at 9 pmol superoxide radical per gram of soil. The protocol includes a cytochrome c-based subprotocol for superoxide radical detection in soils at 770 pmol g(-1) soil. For processing ten samples and depending on the experimental material used (soil or biological), the approximate procedure time would be 2-7 h.

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