Chlorine Dioxide-Pollutant Transformation and Formation of Hypochlorous Acid as a Secondary Oxidant.

Chlorine dioxide (ClO) has been used as a disinfectant in water treatment for a long time, and its use for micropollutant abatement in wastewater has recently been suggested. Surprisingly, a mechanistic understanding of ClO reactions in (waste)water matrices is largely lacking. The present study contributes to this mechanistic understanding by performing a detailed investigation of ClO reactions with organic matter using phenol as a surrogate for reactive phenolic moieties.

Structure of adrenodoxin and function in mitochondrial steroid hydroxylation.

The three-dimensional structure of a truncated mutant of bovine adrenodoxin has been resolved at 1.85 A resolution by MAD. The protein consists of a large core region and a more flexible hairpin loop bearing residues which have been previously described as being involved in redox partner recognition.

New aspects of electron transfer revealed by the crystal structure of a truncated bovine adrenodoxin, Adx(4-108).

Background: Adrenodoxin (Adx) is a [2Fe-2S] ferredoxin involved in steroid hormone biosynthesis in the adrenal gland mitochondrial matrix of mammals. Adx is a small soluble protein that transfers electrons from adrenodoxin reductase (AR) to different cytochrome P450 isoforms where they are consumed in hydroxylation reactions. A crystallographic study of Adx is expected to reveal the structural basis for an important electron transfer reaction mediated by a vertebrate [2Fe-2S] ferredoxin.

Cluster-iron substitution is related to structural and functional features of adrenodoxin mutants and to their redox states.

Site-directed mutants of adrenodoxin were studied for their ability to undergo cluster-iron substitution when reacted with zinc or cadmium salts under non-denaturing conditions in the presence or absence of reductants. Equilibrium and kinetic data for metal substitution were correlated with data on the stability to thermal unfolding and with the redox potential of the protein. Similarly to the wild-type protein, all mutants were able to stabilize a substituted form of the protein containing two metal (Zn or Cd) atoms and two sulfide ions/mol protein and a substituted form of the protein containing two sulfide ions and five Cd atoms/mol protein.

Pro108 is important for folding and stabilization of adrenal ferredoxin, but does not influence the functional properties of the protein.

The truncated mutant Met-adrenodoxin-(4-107)-peptide of bovine adrenal ferredoxin was expressed as apoprotein in Escherichia coli BL21 and could be reconstituted to the holoform by chemical or enzymatic methods. The reconstituted protein had spectroscopic, functional and redox properties similar to the Met-adrenodoxin-(4-108)-peptide of adrenal ferredoxin, into which the cluster was inserted upon expression in the same Escherichia coli strain. Rate of in vitro cluster insertion into the Met-adrenodoxin-(4-107) apoprotein was much lower than for the Met-adrenodoxin-(4-108) apoprotein under identical conditions.