FIGURE 4.

Aberrant pyruvate- and citrate-fueled O₂ consumption by normal mitochondria exogenously enriched with cholesterol. Incubations were performed as described for Figures 3A,B. See text. For cholesterol-loading methodology with normal ACI liver mitochondria (see Parlo and Coleman, 1984). Data error bars are means ± SD. ACI (sham) indicates normal mitochondria treated by the cholesterol loading procedure, but without cholesterol. Normal mitochondria were enriched with three incremental cholesterol levels. The cholesterol content of each enrichment is shown as (μg total cholesterol/mg protein) in parentheses. Inverse correlation between the decrease in pyruvate- and citrate-fueled respiration as the cholesterol enrichment of normal mitochondria is exogenously increased is clear, dramatic and mirrors the respiratory pattern of tumor 3924A mitochondria. Note that respiration fueled by post-aconitate hydratase Krebs/TCA cycle substrates appears to be unaffected by the mitochondrial cholesterol content.