Molecular Architecture of the Inner Membrane of Mitochondria from Rat Liver: A Combined Biochemical and Stereological Study

The molecular structure of mitochondria and their inner membrane has been studied using a combined approach of stereology and biochemistry. The amount of mitochondrial structures (volume, number, surface area of inner membrane) in a purified preparation of mitochondria from rat liver was estimated by stereological procedures. In the same preparation, the oxidative activity of the respiratory chain with different substrates and the concentration of the redox complexes were measured by biochemical means. By relating the stereological and biochemical data, it was estimated that the individual mitochondrion isolated from rat liver has a volume of 0.27 μ m3, an inner membrane area of 6.5 μ m2, and contains between 2,600 (complex I) and 15,600 (aa3) redox complexes which produce an electron flow of over 100,000 electrons per second with pyruvate as substrate. The individual redox complexes and the H+-ATPase together occur at a density of ∼7,500/μ m2 and occupy ∼40% of the inner membrane area. From the respective densities it was concluded that the mean nearest distance between reaction partners is small enough (70-200 Å) to cause the formation of micro-aggregates. The meaning of these results for the mechanism of mitochondrial energy transduction is discussed.