MiP2005: Session 7
Mitochondrial Physiology Network 10.9: 87 (2005) - download pdf
Lysosomal ROS formation.
Hans Nohl, L Gille
Research Inst. Biochemical Pharmacology Toxicology, Veterinary University of Vienna, Veterinärplatz 1, 1210 Vienna, Austria. - email@example.com
Ubiquinone is inhomogenously distributed in subcellular biomembranes. Apart from mitochondria where ubiquinone was demonstrated to exert bioenergetic and pathophysiological functions unusually high levels of ubiquinone were also reported to exist in Golgi vesicles and lysosomes. In lysosomes the interior differs from other organelles by the low pH value which is important not only to arrest proteins but also to ensure optimal activity of hydrolytic enzymes. Since redox‑cycling of ubiquinone is associated with the acceptance and release of protons we assumed that ubiquinone is a part of a redox chain contributing to unilateral proton distribution. A similar function of ubiquinone was earlier suggested by Crane to operate in Golgi vesicles. Support for the involvement of ubiquinone in a presumed couple of redox‑carriers came from our observation that almost 70 % of total lysosomal ubiquinone was in the divalently reduced state. Further reduction was seen in the presence of external NADH. Analysis of the components involved in the transfer of reducing equivalents from cytosolic NADH to ubiquinone revealed the existence of a FAD‑containing NADH‑dehydrogenase. The latter was found to reduce ubiquinone by means of a b‑type cytochrome. Proton translocation into the interior was linked to the activity of the novel lysosomal redox chain. Oxygen was found to be the terminal electron acceptor thereby also regulating acidification of the lysosomal matrix. In contrast to mitochondrial respiration oxygen was only trivalently reduced giving rise to the release of HO·‑radicals. The role of this novel proton‑pumping redox chain and the significance of the associated ROS formation has to be elucidated.
1. Arai K, Kanaseki T, Ohkuma S (1991) Isolation of highly purified lysosomes from rat liver: Identification of electron carrier components on lysosomal membranes. J. Biochem. 110: 541-547.
2. de Vries S, Albracht SP, Berden JA, Slater EC (1981) A new species of bound ubisemiquinone anion in QH2:cytochrome c oxidoreductase. J. Biol. Chem. 256: 11996-11998.
3. Echtay KS, Winkler E, Klingenberg M (2000) Coenzyme Q is an obligatory cofactor for uncoupling protein function. Nature 408: 609-613.
4. Ford T, Graham J, Rickwood D (1994) Iodixanol: A nonionic iso-osmotic centrifugation medium for the formation of self-generated gradients. Anal. Biochem. 220: 360-366.
5. Gille L, Nohl H (2000) The existence of a lysosomal redox chain and the role of ubiquinone. Arch. Biochem. Biophys. 375: 347-354.
6. Graham J, Ford T, Rickwood D (1994) The preparation of subcellular organelles from mouse liver in self-generated gradients of iodixanol. Anal. Biochem. 220: 367-373.
7. Kalen A, Norling B, Appelkvist EL, Dallner G (1987) Ubiquinone biosynthesis by the microsomal fraction from rat liver. Biochim. Biophys. Acta 926: 70-78.
8. Kozlov AV, Nohl H, Gille L (1998) Are reduced ubiquinones oxygen radical generators? Bioorg. Chem. 26: 334-344.
7. Lang J, Gohil K, Packer L (1986) Simultaneous determination of tocopherols, ubiquinols and ubiquinones in blood, plasma, tissue homogenates and subcellular fractions. Anal. Biochem. 1567: 106-116.
8. Lu AY, West SB, Ryan D, Levin W (1973) Characterization of partially purified cytochromes P-450 and P-448 from rat liver microsomes. Drug Metabolism and Disposition 1: 29-39.
9. Mehlhorn RJ, Packer L, Macey R, Balaban AT, Dragutan I (1986) Measurement of transmembrane proton movements with nitroxide spin probes. Methods Enzymol. 127: 738-745.
10. Ohnishi T, King TE (1978) EPR and other properties of succinate dehydrogenase. Methods Enzymol. 53: 483-495.
11. Ohnishi T, Trumpower BL (1980) Differential effects of antimycin on ubisemiquinone bound in different environments in isolated succinate:cytochrome c reductase complex. J. Biol. Chem. 255: 3278-3284.
12. Staniek K, Nohl H (2000) Are mitochondria a permanent source of reactive oxygen species? Biochim. Biophys. Acta 1460: 268-275.