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Humic substances (HS) can be reduced by microorganisms and oxidized by electron acceptors such as Fe(III) or O2. However, redox reactions between HS and highly crystalline Fe(III) minerals and O2 have not yet been quantified. We therefore determined the rates and extent of goethite and hematite reduction by HS in comparison to those of dissolved and poorly crystalline Fe(III) compounds and O2. Although nonreduced HS transferred significant amounts of electrons only to dissolved Fe(III) citrate and ferrihydrite, reduced HS additionally reduced goethite and hematite. The extent of reduction depended on the redox potentials of the Fe(III) compounds. Fewer electrons were transferred from HS to O2 than to Fe(III) despite the more positive redox potential of the O2/H2O redox couple. Reoxidation of reduced HS by O2 took place within minutes and yielded reoxidized HS that were still more reduced than nonreduced HS, indicating that some reduced moieties in HS are protected from reoxidation by O2. Our data suggests (i) reduction of crystalline Fe(III) minerals by reduced HS has to be considered in the environmental electron transfer network, (ii) exposure of reduced HS to O2 does not reoxidize HS completely within short time frames, and therefore, (iii) HS electron shuttling to Fe(III) can occur even in the presence of O2.

1H-3-Hydroxy-4-oxoquinaldine 2,4-dioxygenase (MeQDO) was purified from quinaldine-grown Arthrobacter sp. Ru6la. It was enriched %fold in a yield of 22%, and its properties were compared with 1 H-3-hydroxy-4-oxoquinoline 2,4-dioxygenase (QDO) purified from Pseudomonas putida 3311. The enzyme-catalyzed conversions were performed in an ('80)0,/('60)0, atmosphere. Two oxygen atoms of either ('*O)O, or (l60)O, were incorporated at C2 and C4 of the respective substrates, indicating that these unusual enzymes, which catalyze the cleavage of two carbon-carbon bonds concomitant with CO formation, indeed are 2,4-dioxygenases. Both enzymes are small monomeric proteins of 32 kDa (MeQDO) and 30 kDa (QDO). The apparent K,, values of MeQDO for 1 H-3-hydroxy-4-oxoquinaldine and QDO for lH-3-hydroxy-4-oxoquinoline were 30 pM and 24 pM, respectively. In both 2,4-dioxygenases, there was no spectral evidence for the presence of a chromophoric cofactor. EPR analyses of MeQDO did not reveal any signal that could be assigned to an organic radical species or to a metal, and Xray fluorescence spectrometry of both enzymes did not show any metal present in stoichiometric amounts. Ethylxanthate, metal-chelating agents (tiron, n,d-bipyridyl, 8-hydroxyquinoline, o-phenanthroline, EDTA, diphenylthiocarbazone, diethyldithiocarbamate), reagents that modify sulfhydryl groups (iodoacetamide, N-ethylmaleimide, p-hydroxymercuribenzoate), and reducing agents (sodium dithionite, dithiothreitol, mercaptoethanol j either did not affect 2,4-dioxygenolytic activities at all or inhibited at high concentrations only. With respect to the supposed lack of any cofactor and with respect to the inhibitors of dioxygenolytic activities, MeQDO and QDO resemble aci-reductone oxidase (CO-forming) from Klebsiellu pneumoniae, which catalyzes 1,3-dioxygenolytic cleavage of 1,2-dihydroxy-3-keto-S-methylthiopentene anion ( Chem. 270,[3147][3148][3149][3150][3151][3152][3153]. 1H-3-Hydroxy-4-oxoquinaldine and 1H-3-hydroxy-4-oxoquinoline were reactive towards molecular oxygen in the presence of the base catalyst potassiumtert.-butoxide in the aprotic solvent N,N-dimethylformamide. Base-catalyzed oxidation, yielding the same products as the enzyme-catalyzed conversions, provides a non-enzymic model reaction for 2,4-dioxygenolytic release of CO from 1 H-3-hydroxy-4-oxoquinaldine and 1 H-3-hydroxy-4-oxoquinoline.Keywords: carbon monoxide ; heterocyclic ring cleavage; 3-hydroxy-4( 1H)-quinolone(derivatives) ; 1 H-3-hydroxy-4-oxoquinoline 2,4-dioxygenase (decyclizing, CO-forming) ; 1 H-3-hydroxy-4-oxoquinaldine 2,4-dioxygenase (decyclizing, CO-forming).Arfhrobacfer sp. strain Rii61 a and Pseudomonas putida strain 33/1 utilize quinaldine (2-methylquinoline) and 1H-4-0~0-quinoline, respectively, as sole source of carbon, nitrogen, and energy. In the gram-positive strain Rii61 a, initial hydroxylation

Arsenic is a redox-active metalloid whose toxicity and mobility strongly depends on its oxidation state, with arsenite (As(III)) being more toxic and mobile than arsenate (As(V)). Humic substances (HS) are also redox-active and can potentially react with arsenic and change its redox state. In this study we show that semiquinone radicals produced during microbial or chemical reduction of a HS model quinone (AQDS, 9,10-anthraquinone-2,6-disulfonic acid) are strong oxidants. They oxidize arsenite to arsenate, thus decreasing As toxicity and mobility. This reaction depends strongly on pH with more arsenite (up to 67.3%) being oxidized at pH 11 compared to pH 7 (12.6% oxidation) and pH 3 (0.5% oxidation). In addition to As(III) oxidation by semiquinone radicals, hydroquinones that were also produced during quinone reduction reduced As(V) to As(III) at neutral and acidic pH values (less than 12%) but not at alkaline pH. In order to understand redox reactions between arsenite/arsenate and reduced/oxidized HS, we quantified the radical content in reduced quinone solutions and constructed Eh-pH diagrams that explain the observed redox reactions. The results from this study can be used to better predict the fate of arsenic in the environment and potentially explain the occurrence of oxidized As(V) in anoxic environments.

Endosomal sorting complex required for transport (ESCRT) proteins are involved in a number of cellular processes, such as endosomal protein sorting, HIV budding, cytokinesis, plasma membrane repair, and resealing of the nuclear envelope during mitosis. Here we explored the function of a noncanonical member of the ESCRT-III protein family, the Saccharomyces cerevisiae ortholog of human CHMP7. Very little is known about this protein. In silico analysis predicted that Chm7 (yeast ORF YJL049w) is a fusion of an ESCRT-II and ESCRT-III-like domain, which would suggest a role in endosomal protein sorting. However, our data argue against a role of Chm7 in endosomal protein sorting. The turnover of the endocytic cargo protein Ste6 and the vacuolar protein sorting of carboxypeptidase S (CPS) were not affected by CHM7 deletion, and Chm7 also responded very differently to a loss in Vps4 function compared to a canonical ESCRT-III protein. Our data indicate that the Chm7 function could be connected to the endoplasmic reticulum (ER). In line with a function at the ER, we observed a strong negative genetic interaction between the deletion of a gene function (APQ12) implicated in nuclear pore complex assembly and messenger RNA (mRNA) export and the CHM7 deletion. The patterns of genetic interactions between the APQ12 deletion and deletions of ESCRT-III genes, two-hybrid interactions, and the specific localization of mCherry fusion proteins are consistent with the notion that Chm7 performs a novel function at the ER as part of an alternative ESCRT-III complex.

The utilization of quinaldine (2‐methylquinoline) by Arthrobacter sp. Rü61a proceeds via 1H‐4‐oxoquinaldine, 1H‐3‐hydroxy‐4‐oxoquinaldine, and N‐acetyl‐anthranilic acid. By analogy, 1H‐4‐oxoquinoline is degraded by Pseudomonas putida 33/1 via 1H‐3‐hydroxy‐4‐oxoquinoline and N‐formylanthranilic acid. Using the purified enzymes from both organisms, the mode of N‐heterocyclic ring cleavage was investigated. The conversions of 1H‐3‐hydroxy‐4‐oxoquinaldine and 1H‐3‐hydroxy‐4‐oxoquinoline to N‐acetyl‐ and N‐formylanthranilic acid, respectively, were both accompanied by the release of carbon monoxide. The enzyme‐catalysed transformations were performed in an [18O]O2 atmosphere and resulted in the incorporation of two oxygen atoms into the respective products, N‐acetyl‐ and N‐formylanthranilic acid, indicating an oxygenolytic attack at C‐2 and C‐4 of both 1H‐3‐hydroxy‐4‐oxoquinaldine and 1H‐3‐hydroxy‐4‐oxoquinolone.

Humic substances (HS) are redox-active compounds that are ubiquitous in the environment and can serve as electron shuttles during microbial Fe(III) reduction thus reducing a variety of Fe(III) minerals. However, not much is known about redox reactions between HS and the mixed-valent mineral magnetite (Fe3O4) that can potentially lead to changes in Fe(II)/Fe(III) stoichiometry and even dissolve the magnetite. To address this knowledge gap, we incubated non-reduced (native) and reduced HS with four types of magnetite that varied in particle size and solid-phase Fe(II)/Fe(III) stoichiometry. We followed dissolved and solid-phase Fe(II) and Fe(III) concentrations over time to quantify redox reactions between HS and magnetite. Magnetite redox reactions and dissolution processes with HS varied depending on the initial magnetite and HS properties. The interaction between biogenic magnetite and reduced HS resulted in dissolution of the solid magnetite mineral, as well as an overall reduction of the magnetite. In contrast, a slight oxidation and no dissolution was observed when native and reduced HS interacted with 500 nm magnetite. This variability in the solubility and electron accepting and donating capacity of the different types of magnetite is likely an effect of differences in their reduction potential that is correlated to the magnetite Fe(II)/Fe(III) stoichiometry, particle size, and crystallinity. Our study suggests that redox-active HS play an important role for Fe redox speciation within minerals such as magnetite and thereby influence the reactivity of these Fe minerals and their role in biogeochemical Fe cycling. Furthermore, such processes are also likely to have an effect on the fate of other elements bound to the surface of Fe minerals. Electronic supplementary materialThe online version of this article (doi:10.1186/s12932-017-0044-1) contains supplementary material, which is available to authorized users.

The utilization of quinaldine (2‐methylquinoline) by Arthrobacter sp. Rü61a proceeds via 1H‐4‐oxoquinaldine, 1H‐3‐hydroxy‐4‐oxoquinaldine, and N‐acetyl‐anthranilic acid. By analogy, 1H‐4‐oxoquinoline is degraded by Pseudomonas putida 33/1 via 1H‐3‐hydroxy‐4‐oxoquinoline and N‐formylanthranilic acid. Using the purified enzymes from both organisms, the mode of N‐heterocyclic ring cleavage was investigated. The conversions of 1H‐3‐hydroxy‐4‐oxoquinaldine and 1H‐3‐hydroxy‐4‐oxoquinoline to N‐acetyl‐ and N‐formylanthranilic acid, respectively, were both accompanied by the release of carbon monoxide. The enzyme‐catalysed transformations were performed in an [18O]O2 atmosphere and resulted in the incorporation of two oxygen atoms into the respective products, N‐acetyl‐ and N‐formylanthranilic acid, indicating an oxygenolytic attack at C‐2 and C‐4 of both 1H‐3‐hydroxy‐4‐oxoquinaldine and 1H‐3‐hydroxy‐4‐oxoquinolone.