Redox and chemical activities of the hemes in the sulfur oxidation pathway enzyme SoxAX

Bradley, Justin M., Marritt, Sophie J., Kihlken, Margaret A., Haynes, Kate, Hemmings, Andrew M. ORCID:, Berks, Ben C., Cheesman, Myles R. and Butt, Julea N. ORCID: (2012) Redox and chemical activities of the hemes in the sulfur oxidation pathway enzyme SoxAX. Journal of Biological Chemistry, 287 (48). pp. 40350-40359. ISSN 0021-9258

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SoxAX enzymes couple disulfide bond formation to the reduction of cytochrome c in the first step of the phylogenetically widespread Sox microbial sulfur oxidation pathway. Rhodovulum sulfidophilum SoxAX contains three hemes. An electrochemical cell compatible with magnetic circular dichroism at near infrared wavelengths has been developed to resolve redox and chemical properties of the SoxAX hemes. In combination with potentiometric titrations monitored by electronic absorbance and EPR, this method defines midpoint potentials (Em) at pH 7.0 of approximately +210, −340, and −400 mV for the His/Met, His/Cys−, and active site His/CysS−-ligated heme, respectively. Exposing SoxAX to S2O42−, a substrate analog with Em ∼−450 mV, but not Eu(II) complexed with diethylene triamine pentaacetic acid (Em ∼−1140 mV), allows cyanide to displace the cysteine persulfide (CysS−) ligand to the active site heme. This provides the first evidence for the dissociation of CysS− that has been proposed as a key event in SoxAX catalysis.

Item Type: Article
Faculty \ School: Faculty of Science > School of Chemistry
Depositing User: Users 2731 not found.
Date Deposited: 09 Jan 2013 12:20
Last Modified: 09 Nov 2022 16:30
DOI: 10.1074/jbc.M112.396192

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