Mitochondrial pigments

In each case, however, the oxygen carriers tend to mask the much less abundant mitochondrial pigments. It is not always easy to resolve contributions from endogenous pigments in cell suspensions as the cell density required to give a suitable output is often too large to be compatible with provision of an adequate oxygen supply. 

Azelaic acid is a naturally occurring dicarboxyl-ic acid (1,7-heptanedicarboxylic acid) that has demonstrated beneficial therapeutic effects in the treatment of acne and several disorders of hyperpigmentation [48]. There are minimal effects on normally pigmented human skin, freckles, senile lentigines, and nevi. The cytotoxic and antiproliferative effects of azelaic acid may be mediated via inhibition of mitochondrial ox-idoreductase activity and DNA synthesis. Disturbance of tyrosinase synthesis by azelaic acid may also influence its therapeutic effects. Azelaic acid can be used as a hypopigmenting agent in patients sensitive to hydroquinone. 

Numerous studies have demonstrated that degradation products of (3-carotene exhibit deleterious effects in cellular systems (Alija et al., 2004, 2006 Hurst et al., 2005 Salerno et al., 2005 Siems et al., 2003). A mixture of (3-carotene degradation products exerts pro-apoptotic effects and cytotoxicity to human neutrophils (Salerno et al., 2005 Siems et al., 2003), and enhances the geno-toxic effects of oxidative stress in primary rat hepatocytes (Alija et al., 2004, 2006), as well as dramatically reduces mitochondrial activity in a human leukaemic cell line, K562, and RPE 28 SV4 cell line derived from stably transformed fetal human retinal pigmented epithelial cells (Hurst et al., 2005). As a result of degradation or enzymatic cleavage of (3-carotene, retinoids are formed, which are powerful modulators of cell proliferation, differentiation, and apoptosis (Blomhoff and Blomhoff, 2006). 

Quantitatively minor membrane components with important biological functions include ubiquinone, which is present in the inner mitochondrial membrane, and the tocopherols. Plant chloroplast membranes contain chlorophyll, carotenes, and other lipid-soluble pigments. 

The acetyl-CoA produced in the cytosol from citrate breakdown is used in biosynthetic reactions, including the synthesis of lipids, some amino acids, cofactors, and pigments. This is the only source of acetyl-CoA in the cytosol because the acetyl-CoA produced in the mitochondrion cannot diffuse across the mitochondrial membrane. The NADPH produced indirectly in the cytosol from the citrate is also of great importance in biosynthetic reactions. 

Liang, F.Q., and Godley, B.F. Oxidative stress-induced mitochondrial DNA damage in human retinal pigment epithelial cells A possible mechanism for RPE aging and age-related macular degeneration, Exp. Eye Res., 76,397-403, 2003. 

Widespread (PS light-harvesting assembly pigments plastids) Universal (mitochondrial electron transfer participant) e.g CoQj0... 

Thylakoid membrane as a Molecular Voltmeter and Ammeter. The antibiotic valinomycin was found in 1964 by Moore and Pressman to affect ion transport across the mitochondrial membrane. Subsequently, Pressman and coworkers proposed that valinomycin is an ionophore and acts as a mobile ion carrier across the lipid membrane [cf. sectionlll.B. above]. Since the light-induced FIAC in thylakoid membrane appears to be an electrochromic band shift in pigments produced by an electric field, Boeck and Witt °, Junge and Schmid used this unique effect to probe the effect of compounds such as the ionophore, valinmycin, on the voltage and current density generated across the membrane. 

The reaction center of purple bacteria contains three protein subunits (L, M, and H) located in the plasma membrane (Figure 8-35). Bound to these proteins are the prosthetic groups that absorb light and transport electrons during photosynthesis. The prosthetic groups include a special pair of bacteriochlorophyll a molecules equivalent to the reaction-center chlorophyll a molecules in plants, as well as several other pigments and two quinones, termed Qa and Qb, that are structurally similar to mitochondrial ubiquinone. 

The multiplicity of the cytochrome h components was first shown by Chance (2) in the mitochondrial fragments from beef heart. He suggested the presence of three type h cytochromes The first was characterized as succinate-reducible pigment with an a maximum at 562 nm the second as succinate-reducible in the presence of antimycin, having an a maximum at 566 nm and the third as reducible only by dithionite and having a broad a maximum from 556 to 566 nm. Subsequent studies have also shown the existence of at least two forms of cytochrome h in mitochondria... 

As noted above, cytochrome b in the mammalian respiratory system is firmly bound to the mitochondrial membrane and cannot be solubilized without using detergents such as cholate. It is thus interesting that a cytochrome b-like pigment, cytochrome b-563, is easily extracted from the larvae and pupae of the housefly, Musca domestica, with a simple salt solution, but it cannot be extracted from the adult flies under the same conditions. The cytochrome is obtained as a crystalline preparation after purification by the chromatography on DEAE-cellulose (78,84). The crystalline cytochrome b-563 has a similar spectral property to mammalian cytochrome b and shows absorption peaks at 563, 530, and 428.5 nm in the reduced state. Contrary to purified mammalian cytochrome b, this cytochrome does not combine with carbon monoxide and exists as monomer species in the solution without detergent. 

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