Unknown

Dataset Information

0

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


ABSTRACT: The heme-based chlorite dismutases catalyze the unimolecular decomposition of chlorite (ClO2 -) to yield Cl- and O2. The work presented here shows that chlorite dismutase from Dechloromonas aromatica (DaCld) also catalyzes the decomposition of bromite (BrO2 -) with the evolution of O2 (k cat = (2.0±0.2)×102 s-1; k cat/K M = (1.2±0.2)×105 M-1 s-1 at pH 5.2). Stopped-flow studies of this BrO2 - decomposition as a function of pH show that 1) the two-electron oxidized heme, compound I (Cpd I), is the primary accumulating heme intermediate during O2 evolution in acidic solution, 2) Cpd I and its one-electron reduction product, compound II (Cpd II) are present in varying ratios at intermediate pHs, and 3) only Cpd II is observed at pH 9.0. The pH dependences of Cpd I and Cpd II populations both yield a pK a of 6.7±0.1 in good agreement with the pK a of DaCld activity with ClO2 -. The observation of a protein-based amino acid radical (AA•) whose appearance coincides with that of Cpd II supports the hypothesis that conversion of Cpd I to Cpd II occurs via proton-coupled electron transfer (PCET) from a heme-pocket amino acid to the oxidized porphyrinate of Cpd I to yield a dead-end decoupled state in which the holes decay at different rates. The site of the amino acid radical is tentatively assigned to Y118, which serves as a H-bond donor to propionate 6 (P6). The favoring of Cpd II:AA• accumulation in alkaline solution is consistent with the amino acid oxidation being rate limited by transfer of its proton to P6 having pK a 6.7. Examination of reaction mixtures comprising DaCld and ClO2 - by resonance Raman and electron paramagnetic resonance spectroscopy reveal formation of Cpd II and •ClO2, which forms in preference to the analogous to AA• in the BrO2 - reaction. Addition of ClO- to Cpd II did not yield O2. Together these results are consistent with heterolytic cleavage of the O-BrO- and O-ClO- bonds yielding Cpd I, which is the catalytically active intermediate. The long-lived Cpd II that forms subsequently, is inactive toward O2 production, and diminishes the amount of enzyme available to cycle through the active Cpd I intermediate.

SUBMITTER: Geeraerts Z 

PROVIDER: S-EPMC9328492 | biostudies-literature | 2022 Jul

REPOSITORIES: biostudies-literature

altmetric image

Publications

Roles of High-valent Hemes and pH Dependence in Halite Decomposition Catalyzed by Chlorite Dismutase from <i>Dechloromonas aromatica</i>.

Geeraerts Zachary Z   Stiller Olivia R OR   Lukat-Rodgers Gudrun S GS   Rodgers Kenton R KR  

ACS catalysis 20220706 14


The heme-based chlorite dismutases catalyze the unimolecular decomposition of chlorite (ClO<sub>2</sub> <sup>-</sup>) to yield Cl<sup>-</sup> and O<sub>2</sub>. The work presented here shows that chlorite dismutase from <i>Dechloromonas aromatica</i> (<i>Da</i>Cld) also catalyzes the decomposition of bromite (BrO<sub>2</sub> <sup>-</sup>) with the evolution of O<sub>2</sub> (<i>k</i> <sub>cat</sub> = (2.0±0.2)×10<sup>2</sup> s<sup>-1</sup>; <i>k</i> <sub>cat</sub>/<i>K</i> <sub>M</sub> = (1.2±0.  ...[more]

Shared Molecules

Only show the datasets with similarity scores above: 0.5
     

Similar Datasets

| S-EPMC2909366 | biostudies-literature
| S-EPMC2720342 | biostudies-literature
| S-EPMC126438 | biostudies-literature
| PRJNA9635 | ENA
| S-EPMC7749827 | biostudies-literature
| PRJNA36687 | ENA
| S-EPMC6593283 | biostudies-literature
| S-EPMC9910045 | biostudies-literature
| S-EPMC7665973 | biostudies-literature
| S-EPMC4973843 | biostudies-literature