Roles of High-valent Hemes and pH Dependence in Halite Decomposition Catalyzed by Chlorite Dismutase from .

The heme-based chlorite dismutases catalyze the unimolecular decomposition of chlorite (ClO ) to yield Cl and O. The work presented here shows that chlorite dismutase from (Cld) also catalyzes the decomposition of bromite (BrO ) with the evolution of O ( = (2.0±0.

Structure and reactivity of chlorite dismutase nitrosyls.

Ferric nitrosyl ({FeNO}) and ferrous nitrosyl ({FeNO}) complexes of the chlorite dismutases (Cld) from Klebsiella pneumoniae and Dechloromonas aromatica have been characterized using UV-visible absorbance and Soret-excited resonance Raman spectroscopy. Both of these Clds form kinetically stable {FeNO} complexes and they occupy a unique region of ν(Fe-NO)/ν(N-O) correlation space for proximal histidine liganded heme proteins, characteristic of weak Fe-NO and N-O bonds. This location is attributed to admixed Fe-NO character of the {FeNO} ground state.

Effects of N Binding Mode on Iron-Based Functionalization of Dinitrogen to Form an Iron(III) Hydrazido Complex.

Distinguishing the reactivity differences between N complexes having different binding modes is crucial for the design of effective N-functionalizing reactions. Here, we compare the reactions of a K-bridged, dinuclear FeNNFe complex with a monomeric Fe(N) complex where the bimetallic core is broken up by the addition of chelating agents. The new anionic iron(0) dinitrogen complex has enhanced electron density at the distal N atoms of coordinated N, and though the N is not as weakened in this monomeric compound, it is much more reactive toward silylation by (CH)SiI (TMSI).

Decarboxylation involving a ferryl, propionate, and a tyrosyl group in a radical relay yields heme .

The HO-dependent oxidative decarboxylation of coproheme III is the final step in the biosynthesis of heme in many microbes. However, the coproheme decarboxylase reaction mechanism is unclear. The structure of the decarboxylase in complex with coproheme III suggested that the substrate iron, reactive propionates, and an active-site tyrosine convey a net 2e/2H from each propionate to an activated form of HO Time-resolved EPR spectroscopy revealed that Tyr-145 formed a radical species within 30 s of the reaction of the enzyme-coproheme complex with HO This radical disappeared over the next 270 s, consistent with a catalytic intermediate.

Distinguishing Active Site Characteristics of Chlorite Dismutases with Their Cyanide Complexes.

O-evolving chlorite dismutases (Clds) efficiently convert chlorite (ClO) to O and Cl. Dechloromonas aromatica Cld ( DaCld) is a highly active chlorite-decomposing homopentameric enzyme, typical of Clds found in perchlorate- and chlorate-respiring bacteria. The Gram-negative, human pathogen Klebsiella pneumoniae contains a homodimeric Cld ( KpCld) that also decomposes ClO, albeit with an activity 10-fold lower and a turnover number lower than those of DaCld.