Molecular investigation of iron-sulfur cluster assembly scaffolds under stress.

Fe/S biosynthesis is controlled in Escherichia coli by two machineries, the housekeeping ISC machinery and the SUF system that is functional under stress conditions. Despite many in vivo studies showing that SUF is more adapted for Fe/S assembly under stress, no molecular data supporting this concept have been provided so far. This work focuses on molecular studies of key actors in Fe/S assembly, the SufB and IscU scaffolds under oxidative stress and iron limitation.

Peroxidase-type reactions suggest a heterolytic/nucleophilic O-O joining mechanism in the heme-dependent chlorite dismutase.

Heme-containing chlorite dismutases (Clds) catalyze a highly unusual O-O bond-forming reaction. The O-O cleaving reactions of hydrogen peroxide and peracetic acid (PAA) with the Cld from Dechloromonas aromatica (DaCld) were studied to better understand the Cl-O cleavage of the natural substrate and subsequent O-O bond formation. While reactions with H2O2 result in slow destruction of the heme, at acidic pH heterolytic cleavage of the O-O bond of PAA cleanly yields the ferryl porphyrin cation radical (compound I).

Understanding the roles of strictly conserved tryptophan residues in O2 producing chlorite dismutases.

The chlorite dismutases (Clds) degrade ClO(2)(-) to O(2) and Cl(-) in perchlorate respiring bacteria, and they serve still poorly defined cellular roles in other diverse microbes. These proteins share 3 highly conserved Trp residues, W155, W156, and W227, on the proximal side of the heme. The Cld from Dechloromonas aromatica (DaCld) has been shown to form protein-based radicals in its reactions with ClO(2)(-) and peracetic acid.

Understanding how the distal environment directs reactivity in chlorite dismutase: spectroscopy and reactivity of Arg183 mutants.

The chlorite dismutase from Dechloromonas aromatica (DaCld) catalyzes the highly efficient decomposition of chlorite to O(2) and chloride. Spectroscopic, equilibrium thermodynamic, and kinetic measurements have indicated that Cld has two pH sensitive moieties; one is the heme, and Arg183 in the distal heme pocket has been hypothesized to be the second. This active site residue has been examined by site-directed mutagenesis to understand the roles of positive charge and hydrogen bonding in O-O bond formation.

O(2)-evolving chlorite dismutase as a tool for studying O(2)-utilizing enzymes.

The direct interrogation of fleeting intermediates by rapid-mixing kinetic methods has significantly advanced our understanding of enzymes that utilize dioxygen. The gas's modest aqueous solubility (<2 mM at 1 atm) presents a technical challenge to this approach, because it limits the rate of formation and extent of accumulation of intermediates. This challenge can be overcome by use of the heme enzyme chlorite dismutase (Cld) for the rapid, in situ generation of O(2) at concentrations far exceeding 2 mM.

[The night watchwoman's trolley].

In nursing homes, the presence of a nurse to watch over the residents at night is not required. The residents' sleep is thereby usually in the hands of a nursing assistant and a hospital housekeeper. It is thanks to their skills that they assure the continuity of care and the safety of the elderly people, without overstepping the boundaries of their roles.

How active-site protonation state influences the reactivity and ligation of the heme in chlorite dismutase.

Chlorite dismutase catalyzes O(2) release from chlorite with exquisite efficiency and specificity. The spectroscopic properties, ligand binding affinities, and steady-state kinetics of chlorite dismutase from Dechloromonas aromatica were examined over pH 3-11.5 to gain insight into how the protonation state of the heme environment influences dioxygen formation.