FIG. 7.

The absence of Pnt1p reduces cytochrome c oxidase activity in mitochondria from an S. cerevisiae strain containing wild-type mtDNA. Mitochondria were isolated from mid-log-phase cells of two isogenic strains, DFS188 (PNT1) and SH412 (pnt1Δ::LEU2), that were grown in YPEG at 30°C. The mitochondria were purified on Nycodenz gradients (17) prior to the assay. Specific activity was determined spectrophotometrically as the rate of oxidation of reduced horse heart cytochrome c and is expressed as the change in optical density at 550 nm per minute per milligram of mitochondrial proteins (35). The error bars show the standard deviation of four independent measurements.