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Structural organization of the mitochondrial respiratory chain
Maria Luisa Genova1, Cristina Bianchi, Giorgio Lenaz
1Dipartimento di Biochimica G. Moruzzi, Università di Bologna, Bologna, Italy. mlgenova@biocfarm.unibo.it
The Italian Journal of Biochemistry
|July 2, 2003
Summary
Mitochondrial respiratory chain complexes associate, forming supercomplexes, but also function independently. This suggests a dynamic model where supercomplexes and individual complexes coexist, adapting to cellular metabolic needs.
Area of Science:
- Biochemistry
- Mitochondrial Biology
- Metabolic Control Theory
Background:
- Two models describe mitochondrial respiratory chain organization: random enzyme complex arrangement versus stable super-complex assembly.
- Recent evidence suggests preferential associations, like Complex I with Complex III, supporting a 'respirasome' model with direct electron channeling.
Purpose of the Study:
- To kinetically test and discriminate between the random and super-complex models of the mitochondrial respiratory chain.
- To investigate the functional associations of respiratory complexes using flux control analysis.
Main Methods:
- Digitonin solubilization and Blue Native Polyacrylamide Gel Electrophoresis (PAGE).
- Flux control analysis based on the Metabolic Control Theory, applied to beef heart submitochondrial particles (SMP).
Main Results:
- Enzyme associations involving Complex I and Complex III were observed in the respiratory chain.
- Complex IV appeared randomly distributed, with cytochrome c acting as a mobile electron carrier.
- Flux control analysis indicated no stable functional association between Complex II and Complex III during aerobic succinate oxidation.
- Evidence supports both a diffusible ubiquinone (CoQ) pool and supercomplex formation.
Conclusions:
- Mitochondrial respiratory chain organization is complex, involving both stable supercomplexes and a diffusible ubiquinone pool.
- Supercomplexes likely exist in equilibrium with isolated complexes, dynamically regulated by cellular metabolic conditions.