Biochemical and functional differences in rat liver mitochondrial subpopulations obtained at different gravitational forces

Abstract

Previous studies have reported that liver mitochondria may be fractionated into different subpopulations. However, no careful studies have been performed to exclude mitochondrial damage and to investigate more thoroughly the possible biochemical differences existing between the tip. In this study, we analysed the integrity and the biochemical properties of rat liver a. Mitochondrial fractions were obtained by differential centrifugation at diffiereat gravitational forces: 1000 g (Ml fraction), 3000 g (M3 fraction) and 10,000g (M10 fraction). 11re integrity of these organelles was checked by measuring citrate syMhaae activity both in the presence and absence of Triton X-100 detergent. Biochemical analyses included po determination of cytochrome oxidame activity and respiratory parameters and spectrophotometric determination of cytochrome content. (1) The integrity of a was almost homogeneous between fractions (88.5, 80 and 78.3% in Ml, M3 and M10 fractions, respectively). (2) The heaviest Ml fraction contains mitocin which are on average twee as large as M3 and about three times as large as M10. (3) The Ml fraction exhibited the highest specific cytochrome oxidase activity (1040 ± 20 nAtoms O/min x mg protein) and the highest respiratory rates (72 ± 3 nAtoms O/min x mg protein and 526 ± 45 nAtoms O/min × m protein for States 4 and 3, respectively). Oxidative capacity and respiratory rates decreased as the size of the organelies decreased, reaching values of 1 5 and 1 14 in the M3 and M10 fractions as compared to the Ml. (4) These changes are accompanied by a change in the respiratory control ratio (RCR), which varies from 7.3 in Ml to about 2.0 in M10. A molar trend was observed in cytochrome contents but the differences were not as great as cytochrome oxidese activity and State 3 respiration. These results, as a whole, show that a mitechondrini heterogeneity exists in rat liver cell. We suggest that the above-memioned differences might represent step of mkocbondrW maturation. The maturation would be fundamentally based on the increase of efficiency of the mechanism for ATP synthesis.