Small-volume potentiometric titrations: EPR investigations of Fe-S cluster N2 in mitochondrial complex I

The graphical abstract (from left to right) shows the iron-sulfur cluster N2 in NADH:ubiquinone oxidoreductase (complex I), the EPR-monitored small-volume redox titration by which its reduction potential was determined, and an EPR spectrum of N2 that demonstrates that the cluster has been reduced selectively (no other paramagnetic species are present).68