HAP4-overexpressing cells contain more protein and more cytochromes compared to wild-type cells. (a) Five independent mitochondrial extracts were isolated from logarithmic-phase, glucose-grown wild-type and HAP4 strains. The amount of mitochondrial protein per gram cellular wet weight was determined. (b) Absorption difference spectra of whole-cell suspensions from respiro-fermentative, glucose-repressed wild-type and HAP4-overexpressing cells (YPD) and respiratory grown wild-type cells (YPEG) were obtained using a split-beam spectrophotometer. The cellular content of cytochromes c + c1, b and aa3 was calculated from the difference in absorption between reduced versus oxidized forms of the cytochromes.