Mechanistic Analysis Of Biguanide Induced Inhibition Of Oxidative Phosphorylation

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Kevin Raible Advanced Molecular Biology Final Exam TITLE Mechanistic Analysis of Biguanide-Induced Inhibition of Oxidative Phosphorylation ABSTRACT Biguanide compounds are used clinically to treat a variety of conditions ranging from diabetes to malaria. Despite showing efficacy the underlying mechanisms of how these compounds work is still debated. It has be previously shown biguanides inhibit oxidative phosphorylation, specifically through inhibiting complexes in the electron transport chain. In the current study we tested five clinically relevant biguanides; metformin, phenformin, buformin, proguanil, cycloguanil and begin to elucidate mechanistically how they inhibit mitochondrial function. Our results suggest that all…show more content…
DISCUSSION Our findings demonstrate that all five biguanide compounds tested inhibited oxidative phosphorylation (OP) through an interaction with complex I in the electron transport chain (ETC). Through Electron Paramagnetic Resonance (EPR) analysis we have shown that biguanides do not inhibit the movement of electrons within complex I due to the normal activity of FeS clusters in the presence of the biguanide compounds. We subsequently ruled out competitive inhibition of the ubiquinone-binding site as a possible mechanism, by showing altered Michaelis-Menten kinetics in the presence of decylubiquinone. These data indicate that inhibition is likely a result of an altered catalytic function due to the interaction between the compounds and complex I. Biguanide-dependent inhibition of complex I isolated from mammalian, yeast, and bacterial sources indicates a conserved target of action. We hypothesized that biguanide inhibition may be occurring at the enzymatic moiety of the matrix-facing ND3 subunit of complex I; where NADH oxidation occurs facilitating the transmembrane transfer of hydrogen and the inter-ETC-complex electron exchange. A specific residue, Cys39, located in an amphipathic region between the redox and proton-transfer domains is particularly important in determining the functional confirmation of the protein. The presence or absence of substrate is responsible for either the ‘closed’ active confirmation, or the ‘open’
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