Cytochrome reduced synthesis

Reduced synthesis. The synthesis of enzymes may be decreased, resulting in a decrease in the in vivo activity. With cytochrome P-450 there are a number of ways in which this occurs. Thus, administration of the metal cobalt to animals will decrease levels of cytochromes P-450 by inhibiting both the synthesis and increasing the degradation of the enzyme. Thus, cobalt inhibits S-aminolaevulinic acid synthetase, the enzyme involved in heme synthesis. Cobalt will also increase the activity of heme oxygenase, which breaks down the heme portion to biliverdin. The compound 3-amino, 1, 2, 3-triazole decreases cytochromes P-450 levels by inhibiting porphyrin synthesis. 

FIGURE 22.17 The R. viridis reaction center is coupled to the cytochrome h/Cl complex through the quinone pool (Q). Quinone molecules are photore-duced at the reaction center Qb site (2 e [2 hv] per Q reduced) and then diffuse to the cytochrome h/ci complex, where they are reoxidized. Note that e flow from cytochrome h/ci back to the reaction center occurs via the periplasmic protein cytochrome co- Note also that 3 to 4 are translocated into the periplasmic space for each Q molecule oxidized at cytochrome h/ci. The resultant proton-motive force drives ATP synthesis by the bacterial FiFo ATP synthase. (Adapted from Deisenhofer, and Michel, H., 1989. The photosynthetic reaction center from the purple bac-terinm Rhod.opseud.omoaas viridis. Science 245 1463.)... 

The cytochrome b(6)f complex mediates electron transfer between the PSI and PSII reaction centers by oxidizing hpophUic plastoquinol (PQH2) (see Figure 7.24) and reducing the enzymes plastocyanin or cytochrome Ce. The electronic connection also generates a transmembrane electrochemical proton gradient that can support adenosine triphosphate (ATP) synthesis instead of electron transport. 

Most compounds oxidized by the electron transport chain donate hydrogen to NAD+, and then NADH is reoxidized in a reaction coupled to reduction of a flavoprotein. During this transformation, sufficient energy is released to enable synthesis of ATP from ADP. The reduced flavoprotein is reoxidized via reduction of coenzyme Q subsequent redox reactions then involve cytochromes and electron transfer processes rather than hydrogen transfer. In two of these cytochrome redox reactions, there is sufficient energy release to allow ATP synthesis. In... 

Because photosystem 11 and the cytochrome b/f complex release protons from reduced plastoquinone into the lumen (via a Q. cycle), photosynthetic electron transport establishes an electrochemical gradient across the thylakoid membrane (see p. 126), which is used for ATP synthesis by an ATP synthase. ATP and NADPH+H", which are both needed for the dark reactions, are formed in the stroma. 

In one-, four- and 13-week studies, the effects of coumarin treatment were compared in male Sprague-Dawley rats, CD-I mice and Syrian hamsters. Rats were fed 0-0.75% coumarin for one and four weeks and 0.5% coumarin for 13 weeks. Mice and hamsters were fed 0-0.5 and 0-1.0% coumarin, respectively, for one, four or 13 weeks. In the rat, coumarin caused dose-related hepatotoxic effects which included vacuolar degeneration, apoptosis and bile duct proliferation and increases in serum bilirubin content and both serum and hepatic y-glutamyltranspeptidase activity. A sustained stimulation of hepatocyte replicative DNA synthesis was observed in rats treated for four and 13 weeks. Levels of total hepatic glutathione were increased approximately twofold, and there were statistically significant decreases in microsomal cytochrome P450 content and ethylmorphine 7V-demethylase activity. These effects were reduced or not observed in mice and hamsters (Lake Grasso, 1996). 

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