Temperature-dependent ESR and computational studies on antiferromagnetic electron transfer in the yeast NADH dehydrogenase Ndi1Electronic supplementary information (ESI) available. See DOI: 10.1039/c6cp08107j

Ndi1 is a special type-II complex I nicotinamide-adenine-dinucleotide (NADH):ubiquinone (UQ) oxidoreductase in the yeast respiratory chain, with two bound UQs (UQ I and UQ II ) mediating electron transfer from flavin cofactors to ubiquinone, in the absence of Fe-S chains. Here, we elucidate the underlying mechanism of electron transfer in Ndi1 through temperature-dependent Electron Spin Resonance (ESR) experiments in conjunction with quantum chemical calculations. It is revealed that electron transfer is mediated by antiferromagnetic (AFM) interactions between flavin-adenosine-dinucleotide (FAD) and UQ I and between UQ I and UQ II . The π-stacking interactions among the aromatic complexes also enhance the through-space electron transfer. The FAD/UQ I pair works as a rectifier converting double-electron co-transfer into sequential single-electron transfer events. The results not only expand our understanding on the observed AFM interactions among p-orbital aromatic mixed-stack in proteins, but also provide significant insights into the fabrication of materials with special magnetic properties using biological samples. The electron transfer mechanism of Ndi1.