Fig. 1.

A representation of CI showing the hydrophilic matrix and hydrophobic membrane arms/domains oriented almost perpendicularly to each other. NADH donates its electrons to the flavin mononucleotide (FMN) prosthetic group located at the tip of the matrix arm. The matrix arm has eight Fe–S clusters, seven of which are involved in transferring electrons from FMN to Ubiquinone. The Fe–S cluster adjacent to the FMN molecule (cluster N1a) has been proposed to be essential for maintaining the structure around the FMN site, but is not involved in electron transport. A central axis of polar residues that have been hypothesized to be involved in driving proton translocation across the membrane arm is also shown. The + and − signs in the membrane domain denote the presence of polar amino acids and are not meant to show the number or distribution pattern of charged amino acids in the central axis