2wp9

Publication Abstract from PubMed

Succinate-ubiquinone oxidoreductase (SQR) and menaquinol-fumarate oxidoreductase (QFR) from Escherichia coli are members of the complex II family of enzymes. SQR and QFR catalyze similar reactions with quinones, however, SQR preferentially reacts with higher potential ubiquinones and QFR with lower potential napthoquinones. Both enzymes have a single functional quinone-binding site proximal to a [3Fe-4S] iron-sulfur cluster. A difference between SQR and QFR is that the redox potential of the [3Fe-4S] cluster in SQR is 140 mV higher than that found in QFR. This may reflect the character of the different quinones with which the two enzymes preferentially react. To investigate how the environment around the [3Fe-4S] cluster affects its redox properties and catalysis with quinones a conserved amino acid proximal to the cluster was mutated in both enzymes. It was found that substitution of SdhB His207 by threonine (like found in QFR) resulted in a 70 mV lowering of the redox potential of the cluster as measured by EPR. The converse mutation in QFR raised the redox potential of the cluster. X-ray structural analysis suggests that placing a charged residue near the [3Fe-4S] cluster is a primary reason for the alteration in redox potential with the hydrogen-bonding environment having a lesser effect. Steady state enzyme kinetic characterization of the mutant enzymes shows that the redox properties of the [3Fe-4S] cluster has only minor effect on catalysis.

Perturbation of the quinone binding site of complex II alters the electronic properties of the proximal [3Fe-4S] iron-sulfur cluster.,Ruprecht J, Iwata S, Rothery RA, Weiner JH, Maklashina E, Cecchini G J Biol Chem. 2011 Feb 10. PMID:21310949^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.