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Title: Flavocytochrome b₂ : molecular recognition
Author: Welsh, Fraser E.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1998
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Flavocytochrome b2 from Saccharomyces cerevisiae is a L-lactate:cytochrome c oxidoreductase found in the mitochondrial intermembrane space. The crystal structure has been solved to 2.4Å resolution showing the enzyme to be a homotetramer (Mr 230 000). Each subunit (511 amino acids) is composed of two domains: A cytochrome domain containing protohaem IX (residues 1-100); and a flavodehydrogenase domain, FDH, which contains FMN (residues 101-511). The two domains are tethered by a "hinge" region (residues 92-103). In the crystal structure residues 295-311 are highly disordered and so not visible. This region is a proteolytically sensitive loop for which a function has not yet been determined. Flavocytochrome b2 has been fully characterised and shown to be a "biological transformer" accepting electrons from a strictly 2-electron donor, L-lactate, and passing them individually to a 1-electron acceptor, cytochrome c. FDH has been independently expressed in E.coli allowing accurate characterisation of its properties without interference from the intense absorbance of the cytochrome domain. This has shown that although FDH remains an efficient L-lactate dehydrogenase, it has negligible cytochrome c reductase activity. This is intriguing as the thermodynamic driving force for electron transfer from FDH to cytochrome c, as determined from reduction potentials, is greater than 1/3V. We believe a lack of inter-protein recognition between the two proteins prevents them forming an effective electron transfer complex. The aim of this work was to alter the electron acceptor specificity of FDH to favour interactions with positively charged molecules.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available