Hi, I am Mirjam,

I am interested in understanding the electron transfer mechanism of respiratory complex I in strictly anaerobic bacteria. Complex I is the first enzyme in many respiratory chains, where it couples the oxidation of NADH with the translocation of protons across the membrane. This process is crucial for generating the proton gradient that powers ATP synthesis.

In anaerobic bacteria like Geobacter metallireducens, respiratory complex I uses menaquinone (MK) instead of ubiquinone as the electron acceptor. Since MK has a significantly lower redox potential (E°’ = –74 mV vs. +100 mV), this redox reaction yields less energy, potentially reducing the number of protons that can be pumped. Yet, these organisms still manage to grow efficiently.

I aim to uncover how MK-dependent respiratory complex I maintains energy efficiency despite this thermodynamic constraint — and to explore the specific metabolic and electron transfer pathways that support this mechanism.

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Alternative tricarboxylic acid (TCA) cycle and proposed mechanism of respiratory complex I from Geobacter metallireducens, shown using its AlphaFold 2 structure.