SDS–PAGE analysis of mitochondrially encoded subunits of CcO and its pressure-generated subcomplexes. Monomeric CcO, after exposure to 3 kbar of hydrostatic pressure for 2 h, was separated by HiTrapQ anion-exchange chromatography into three distinct chromatographic species, i.e., A, B, and C as described in the legend of Figure 4. The subunit content of CcO eluting in peaks B and C was compared to the subunit content of CcO that had not been exposed to hydrostatic pressure (CcO Control), which is identical to CcO peak A (27). The relative amounts of subunits I–IV in each sample were determined by SDS–PAGE using a 15% running gel that contained 2 M urea and 0.1% SDS. Gels were stained, destained, and scanned as described in Experimental Procedures. Data are representative of analyses done in triplicate.