Figure 6.

Mitochondrial respiratory chain function in Mclk1 knockout liver. (A) Liver mitochondria of Mclk1^liver-KO mice (Mclk1^loxP/−, AlbCre+) exhibit accumulation of DMQ₉ along with a dramatic reduction in UQ₉ content compared with that in Mclk1^loxP/− controls. Columns show the mean ± SEM of peak areas on HPLC chromatographs normalized to protein content. Mitochondrial UQ₉ concentrations expressed also as nmol/mg mitochondrial protein, are reduced by an average of 85% in the KO livers compared with controls. n = 8 littermate pairs for 8-month data and 10 littermate pairs for 15-month data. (B) Mclk1 knockout liver displays a mild reduction in mitochondrial state 3 respiration rates. State 3 respiration rates with Complex I-linked substrates, glutamate plus malate, are 8% (8-month-old) to 13% (15-month-old) lower than their respective littermate controls (Mclk1^loxP/−). Complex II-dependent respiration, measured with succinate plus rotenone, is decreased by 14% (8-month-old) to 18% (15-month-old). In both control and knockout liver, there seems to be a trend toward a decrease with age, but it is not statistical significant. Columns represent mean values ± SEM of eight to nine mice per group. (C) Enzymatic activities of respiratory complexes in isolated liver mitochondria. The integrated activity of Complex II + III is significantly decreased in the liver mitochondrial preparation from Mclk1^liver-KO mice (15-month-old), whereas the activities of individual complexes are unaltered compared with Mclk1^loxP/− controls. Columns represent the mean enzymatic activities ±SEM of 11–14 mice. Significant differences were compared with controls by paired t-test. *P < 0.05, **P < 0.01 and ***P < 0.001.