Kinetic gating by an iron sulfur chain modulates flavin radical-pair spin chemistry in mitochondrial Complex I

In human mitochondrial Complex I, coupling the flavin oxygen radical pair to an eight-iron-sulfur-cluster chain shows proximal clusters kinetically gate the singlet yield via electron-transfer competition.

• Why it matters: Existing radical-pair models isolate the flavin, but Complex I physically wires it to an iron-sulfur chain, potentially changing spin-dependent reaction pathways.
• What they did: Using the human Complex I structure and open quantum system models, the authors simulated spin coupling and electron transfer across the eight-cluster network to track singlet yield and coherence decay.
• The result: Spin coherence decays rapidly along the chain, while downstream clusters shift the calculated singlet yield when transfer rates compete with recombination; effects require superoxide spin relaxation slower than free solution.

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