High affinity cation-binding sites in Complex I from Escherichia coli

Studies on the activity of Complex I from Escherichia coli in the presence of different metal cations revealed at least two high affinity metal-binding sites. Membrane-bound or isolated Complex I was activated by K+ (apparent binding constant ∼ 125 μM) and inhibited by La3+ (IC50 = 1 μM). K+ and La3+ do not occupy the same site. Possible localization of these metal-binding sites and their implication in catalysis are discussed.