Protein, flavo

The reduction of flavin in FAD is accompanied by loss of the characteristic yellow colour. The reduction-oxidation of flavo-proteins can thus be followed spectro-photomelrically. 

This impressive reaction is catalyzed by stearoyl-CoA desaturase, a 53-kD enzyme containing a nonheme iron center. NADH and oxygen (Og) are required, as are two other proteins cytochrome 65 reductase (a 43-kD flavo-protein) and cytochrome 65 (16.7 kD). All three proteins are associated with the endoplasmic reticulum membrane. Cytochrome reductase transfers a pair of electrons from NADH through FAD to cytochrome (Figure 25.14). Oxidation of reduced cytochrome be, is coupled to reduction of nonheme Fe to Fe in the desaturase. The Fe accepts a pair of electrons (one at a time in a cycle) from cytochrome b and creates a cis double bond at the 9,10-posi-tion of the stearoyl-CoA substrate. Og is the terminal electron acceptor in this fatty acyl desaturation cycle. Note that two water molecules are made, which means that four electrons are transferred overall. Two of these come through the reaction sequence from NADH, and two come from the fatty acyl substrate that is being dehydrogenated. 

D-Ribose Nucleic acids. Structural elements of nucleic acids and coenzymes, eg, ATP, NAD, NADP, flavo-proteins. Ribose phosphates are intermediates in pentose phosphate pathway. ... 

Stevenson, R.C., Dunham, W.R., Sands, R.H., Singer, T.P., and Beinert, H. 1986. Studies on the spin-spin interaction between flavin and iron-sulfur cluster in an iron-sulfur flavo-protein. Biochimica et Biophysica Acta 869 81-88. 

NAD PI I gives up hydrogen atoms to the flavo protein NADPH— cytochrome P450 reductase and becomes NADP+. The reduced flavo protein transfers these reducing equivalents to cytochrome P450. The reducing... 

Fluorescence occurs when radiant energy is absorbed and then, almost instantly, some of the energy is re-emitted, usually at a longer wavelength. Primary fluorescence (autofluorescence) occurs in flavo-proteins (13), plant cell wall materials such as lignin (7), and in flagella (14). Secondary fluorescence is when a material binds a fluorescent dye... 

A more detailed breakdown of the fold abundance by individual genomes shows the same trends, as well as a number of unique features (Fig. 6, see color insert). The latter include, for example, the marked overrepresentation of Rossmann-fold domains in Mycobacterium, flavo-doxins in Synechocystis and methyltransferases in Helicobacter. Furthermore, the differences in fold distribution between the multicellular eukaryote Caenorhabditis elegans and the unicellular yeast become readily apparent. In the nematode, the protein kinases are the most common fold, with the P-loops relegated to the second position in contrast, the yeast distribution is more similar to that seen in prokaryotes (Fig. 6). 

Figure 4. Typical GLC of lindane photodegradation by protease-liberated flavo-protein from TX-20 algae (A), TX-20 (B), TX-20 FMN (C), phosphate buffer (D), phosphate buffer FMN Rt for y-BTC — 2.3 min and y-BHC = 9.7 min.

Photodegradation of DDT by the protease-liberated flavo-protein from TX-20 resulted in the formation of TDE as the major product in addition to three other minor compounds. It has been well established that DDT conversion to TDE, anaerobically, is a reductive process involving replacement of a chlorine atom by hydrogen. On the other hand, it has been suggested that photo-lytic reactions involve a charge transfer from an amine to DDT and a subsequent pickup of a proton. Thus there is a possibility that the photochemical reaction involving flavoproteins undergoes a similar reaction scheme. Much more data are, however, needed to confirm this point. 

Cytochrome P450, subfamily lie (mepheny-toin 4-hydroxylase), polypeptide 19 flavo-protein-hnked monooxygenase mephenytoin 4 -hydroxylase microsomal monooxygenase xenobiotic monooxygenase... 

I. 6.99.3]. NADH dehydrogenase [EC 1.6.99.3] catalyzes the reaction of NADH with an acceptor to produce NAD+ and the reduced acceptor. Iron-sulfur and flavo-proteins are still being used as cofactors with this component of EC 1.6.5.3. Interestingly, after certain preparations have been followed, cytochrome c may serve as the acceptor substrate. 

This iron-sulfur oxygenase [EC 1.14.12.11] catalyzes the reaction of molecular oxygen with toluene and NADH to produce (15 ,27 )-3-methylcyclohexa-3,5-diene-l,2-diol and NAD. This reductase is an iron-sulfur flavo-protein (FAD) that contains ferredoxin. Ethylbenzene, 4-xylene, and some halogenated toluenes can likewise undergo conversion to the corresponding cw-dihydro-diols. 

In conclusion, spectacular advances in the fields of flavonoid bioavailability and flavo-noid-mediated cell effects in relation to the development of new biological tools (e.g., proteomic analysis, reporter genes) have been achieved during the last decade. A more coherent picture of the ways flavonoids combine their redox properties and affinity to specific proteins is emerging. This wealth of new chemical and biological information suggests that the elucidation of in vivo molecular mechanisms and receptors involved in flavonoid health effects is at hand. 

Flavohydroquinone bound to apoproteins plays a very important role in flavo-protein-catalysis, either in the electron-transfer to substrates or other enzymes or in the oxygen activation reaction. The chemical reactivity of 1,5-dihydroflavin bound to apoproteins can differ drastically from that of free flavin. The reactivity is likely governed by factors such as the conformation of the bound flavohydroquinone and the ionization state (cf. below). 

Propionibacteria can produce pyruvate either from glucose, primarily via the EMP pathway, or from oxidation of lactate by using a flavo-protein as a hydrogen acceptor (Gottschalk 1979). As shown in Figure... 

Still another difference between biosynthesis of fatty acids and oxidation (in mammals) is that the former has an absolute requirement for NADPH (Fig. 17-12) while the latter requires NAD+ and flavo-proteins (Fig. 17-1). This fact, together with many other observations, has led to the generalization that biosynthetic reduction reactions usually require NADPH rather than NADH. Many measurements have shown that in the cytosol of eukaryotic cells the ratio [NADPH]/[NADP+] is high, whereas the ratio [NADH]/[NAD+] is low. Thus, the NAD+/NADH system is kept highly oxidized, in line with the role of NAD+ as a principal biochemical oxidant, while the NADP+/NADPH system is kept reduced. 

The b cytochromes and cytochrome c, fit into this scheme between reducing substrates and cytochrome c. The idea thus developed that the respiratory apparatus includes a chain of cytochromes that operate in a defined sequence. The next question was whether the cytochromes are all bound together in a giant complex, or whether they diffuse independently in the membrane. Before we address this point, we need to consider three other types of electron carriers that participate in the electron-transport chain flavo-proteins, iron-sulfur proteins, and ubiquinone. 

Quinoprotein dehydrogenases containing PQQ or TTQ have been shown to function in various microorganisms in addition to the NAD(P)-dependent and flavo-protein dehydrogenases. The PQQ-containing dehydrogenases require Ca (or Mg) for structural as well as catalytic purposes. However, the mechanism of activation of PQQ, the substrate or the hemiketal adduct by the metal ion, is still unknown. 

Harborne and Saleh (1971) confirmed the presence of quercetin 3-arabinoside in the leaves of fennel and three other flavo-nol glycosides, kaempferol 3-arabinoside, kaempferol 3-glucuronide and quercetin 3-glucuronide. A chemotypic characterization of populations of fennel based on the occurrence of glycosides has been attempted. The dried distillation residue of fennel fruits contains 14-22% protein and 12-18% fat and is suitable for stock feed (Weiss, 2002). 

FIGURE 17. Electron transfer pathways in FCSD. Through-space jumps are indicated hy dotted lines and paths along hydrogen bonds are indicated by dashed lines. Four paths (ln4) with decreasing electronic coupling are indicated. Fp and Cy indicate residues in the flavo-protein and the cytochrome subunits, respectively. 

Mathews, F. S., Chen, Z.-w., Meyer, T. E., Cusanovich, M. A., Koh, M., Cusanovich, M. A., and Van Beeumen, J. J., 1996, structural studies of flavocytochrome c sulfide dehydrogenase from the purple phototrophic bacterium Chromatium vinosum, in Flavins and Flavo-proteins 1996 (K. J. Stephens, V. Massey, and C. H. Williams, eds.). University of Calgary Press, Calgary, 913n916. 

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