Intersubunit interactions in the bovine mitochondrial complex I as revealed by ligand blotting

Bovine mitochondrial complex I (NADH: ubiquinone oxidoreductase) is composed of 3 structural domains, designated FP (flavoprotein, 3 subunits), IP (iron-sulfur protein, 7-8 subunits) and HP (hydrophobic protein, > 30 subunits). IP intervenes between FP and HP, and in complex I its 75 kDa subunit appears to interact with the 51 kDa subunit of FP. In this study, we show by the technique of ligand blotting that isolated IP binds (a) only to the 51 kDa subunit of FP, and (b) to the 42, 39, 23, 20 and 16 kDa subunits of HP. Because a 23 kDa and a 20 kDa subunit of complex I are potential iron-sulfur proteins, these and our previous results are consistent with the following possible path of electrons in complex I: NADH-->51 and 24 kDa subunit of FP-->75 kDa subunit of IP-->23 and 20 kDa subunits of HP-->ubiquinone.