Complex I is composed of 45 subunits in mammals, organized into a distinct L-shaped structure. The hydrophilic domain extends into the mitochondrial matrix and contains the redox centers, including FMN and multiple Fe-S clusters. The hydrophobic domain is embedded in the inner mitochondrial membrane and is involved in proton translocation. This intricate architecture underpins the enzyme’s ability to couple electron transfer with proton pumping, a process known as chemiosmotic coupling.
