The role of a conserved tyrosine in the 49-kDa subunit of complex I for ubiquinone binding and reduction.

摘要: Abstract Iron–sulfur cluster N2 of complex I (proton pumping NADH:quinone oxidoreductase) is the immediate electron donor to ubiquinone. At a distance only ∼ 7 A in 49-kDa subunit, highly conserved tyrosine found at bottom previously characterized quinone binding pocket. To get insight into function this residue, we have exchanged it for six different amino acids from Yarrowia lipolytica. Mitochondrial membranes all mutants contained fully assembled that exhibited very low dNADH:ubiquinone oxidoreductase activities with n-decylubiquinone. With most conservative exchange Y144F, no alteration paramagnetic resonance spectra was detectable. Remarkably, high were observed ubiquinones Q1 and Q2 coupled proton pumping. Apparent Km values markedly increased pronounced resistance inhibitors decyl-quinazoline-amine (DQA) rotenone. We conclude Y144 directly binds head group ubiquinone, likely via hydrogen bond between aromatic hydroxyl ubiquinone carbonyl. This places substrate an ideal its iron–sulfur efficient transfer during catalytic cycle I.