Fig. 4.

MS of intact CcO reveals stabilization of monomeric/dimeric CcO by associated lipids. After exchanging DM detergent for C₈E₄ detergent (Upper) the CcO complex remains intact and the MS reveals peak series for monomeric (blue circles) and dimeric (gray circles) CcO. Charge states for the most intense peak of each series are given. Observed masses of the monomer (215 kDa) and dimer (435 kDa) are higher than the theoretical masses calculated from subunit masses, consistent with the association of lipids in monomeric and dimeric CcO. The broad peak width of the charge states is assigned to multiple lipid bound states and heterogeneous PTMs.