Steady-state levels of complex I subunits in the 13.4L and the nuo13.4×L mutants determined by Western blotting. Subunits 20.9, 20.8, 14, 12.3, and 9.8 kDa are components of the membrane arm whereas subunits 78, 51, 30.4, 29.9, 21.3a, 21.3c, 21, 18.4, 13.4, and 10.5 kDa are present in the peripheral domain of the enzyme.