Physiological diversity of mitochondrial oxidative phosphorylation

Abstract

To investigate the physiological diversity in the regulation and control of mitochondrial oxidative phosphorylation, we determined the composition and functional features of the respiratory chain in muscle, heart, liver, kidney, and brain. First, we observed important variations in mitochondrial content and infrastructure via electron micrographs of the different tissue sections. Analyses of respiratory chain enzyme content by Western blot also showed large differences between tissues, in good correlation with the expression level of mitochondrial transcription factor A and the activity of citrate synthase. On the isolated mitochondria, we observed a conserved molar ratio between the respiratory chain complexes and a variable stoichiometry for coenzyme Q and cytochrome c, with typical values of [1–1.5]:[30–135]:[3]:[9–35]:[6.5–7.5] for complex II:coenzyme Q:complex III:cytochrome c:complex IV in the different tissues. The functional analysis revealed important differences in maximal velocities of respiratory chain complexes, with higher values in heart. However, calculation of the catalytic constants showed that brain contained the more active enzyme complexes. Hence, our study demonstrates that, in tissues, oxidative phosphorylation capacity is highly variable and diverse, as determined by different combinations of 1) the mitochondrial content, 2) the amount of respiratory chain complexes, and 3) their intrinsic activity. In all tissues, there was a large excess of enzyme capacity and intermediate substrate concentration, compared with what is required for state 3 respiration. To conclude, we submitted our data to a principal component analysis that revealed three groups of tissues: muscle and heart, brain, and liver and kidney.

Effects of cadmium chloride on some mitochondria-related activity and gene expression of human MDA-MB231 breast tumor cells

“…We therefore studied the expression of some subunits of this complex in our experimental model system and we found that the levels of COXII and COXIV mRNAs and proteins remained constant after 24-h exposure, while they decreased after longer incubations (96-h). It is noteworthy that the lack of physiologic amounts of some COX subunits did not influence the mitochondrial energetic rate, however, it must be taken into account that in all tissues studied, the enzyme content was in a large excess compared with what is required for state 3 respiration [63]. Hypothetically, the reduction of the amount of COX subunits could be related to ROS production since mitochondrial proteins are often among the first targets of ROS attack in cells because of their immediate proximity to the ROS-generating sources [64].…”

Mitochondrial complex I dysfunction induced by cocaine and cocaine plus morphine in brain and liver mitochondria

“…It is known that different tissues have different mitochondrial respiratory chain content, composition, activity and respiration velocity at state 3 (Benard et al, 2006). Brain mitochondria have the highest ATP production rate with complex I substrates, compared to heart and liver mitochondria, possibly related with their limited defenses against reactive oxygen species (ROS).…”

Time course of mitochondrial metabolism alterations to repeated injections of bupivacaine in rat muscle

“…12 For instance, the citrate synthase activity decreased by 50% in rats subjected to bupivacaine injections for 112 hr, and mitochondrial adenosine diphosphate-stimulated oxygen consumption measured in situ was further reduced by 80% when compared with the control group. In a previous study, we discussed the different modes of bupivacaine inhibition of mitochondrial energy metabolism, 4,15 including 1) the specific inhibition of mitochondrial respiratory chain complex I (as observed on isolated mitochondria); 2) OXPHOS uncoupling; 3) the specific inhibition of the mitochondrial F1-F0-ATP synthase; 4) the decrease of mitochondrial membrane electric potential; 5) the fragmentation of the mitochondrial network; and 6) the possible onset of mitoptosis.…”

“…Previous studies in rat tissues demonstrated that the activity of citrate synthase is proportional to the protein content of respiratory chain complexes measured by Western blot. 12 In our study, we measured the citrate synthase activity to understand whether the observed changes in mitochondrial oxygen consumption could be attributed to changes in the mitochondrial content.…”

“…Also, the citrate synthase activity is typically used to evaluate the mitochondrial content in muscle for the diagnosis of mitochondrial disease. 12 For the enzymatic measurement of citrate synthase activity, about 60 mg of psoas or gracilis muscle was minced and homogenized with a glass Potter homogenizer in ice-cold medium (10% w/v) containing 225 mM mannitol, 75 mM sucrose, 10 mM Tris-HCl, 0.10 mM EDTA, pH 7.2. The homogenate was then centrifuged for 20 min at 650 g. The supernatant was collected and the protein concentration was determined.…”