Flavoprotein table

Nevertheless, there is good evidence that in all purely bluelight sensitive organisms, the photoreceptor is a flavin (flavoprotein) (Table 2), which appears to be bound to membranes (plasmalemma) in a highly dichroic manner. The mechanism of sensory transduction is probably correlated with light-induced redox reactions mediated by a flavin. This observation is consistent with the fact that nearly all physiolog-... 

The primary process for the oxidation by O2 - of dihydrophenazine and dihydro-lumiflavin must be analogous to that for PhNHNHPh (Scheme 7-14) to give the anion radicals of phenazine (Phen ) and lumiflavin (Fl ). These in turn react with O2 to give O2 - plus phenazine and lumiflavin, respectively the process is analogous to that for the anion radical of azobenzene (PhN NPh), The oxidation potentials (Ep,a) for PhN NPh, Phen - and Fl - in Me2SO are -1.1 V versus NHE, -0.9 V, and -0.6 V, respectively. Each value is sufficiently negative to reduce O2 to O2 - (-0.5 V versus NHE in Me2SO). Hence, the (O2 )-induced auto-oxidation of PhNHNHPh also is thermodynamically feasible for dihydrophenazine and dihydro-lumiflavin and does occur for these two model substrates of reduced flavoproteins (Table 7-3). Such an auto-oxidation reaction sequence may be relevant to the fractional yield of 02 - from the flavin-mediated activation of 02 ° and the auto-oxidation of xanthine [catalyzed by xanthine oxidase (XO), a flavoprotein]. ... 

Protein fixation . Massey et al. (121) were the first to investigate systematically bioradical formation by comparative enzymology of flavoproteins . It turned out that flavoproteins can be divided into two classes according to whether their radicals are blue or red. Moreover and quite surprisingly, it became obvious that all red radical flavoproteins were 2/2-flavoproteins (Table 1, cf. above), while the blue radical flavoproteins happened to be either 1/1-, 2/1- or 1/2-flavoproteins. In other words All flavoproteins involved essentially with le -transfer (either by input or by output or by both) have blue radicals. Massey and Palmer referred to the blue radical flavoproteins as dehydrogenases and to... 

Reduction potentials can also be quite sensitive to molecular environment. The influence of environment is especially important for flavins, such as FAD/FADHg and FMN/FMNHg. These species are normally bound to their respective flavoproteins the reduction potential of bound FAD, for example, can be very different from the value shown in Table 21.1 for the free FAD-FADHg couple of —0.219 V. A problem at the end of the chapter addresses this... 

Substrate Spectra. Photodecomposition of five insecticidal chemicals stimulated by protease-liberated flavoprotein was studied and results are shown in Tables II and III and Figures 3, 4 and 5. Generally the flavoprotein(s) was significantly more active in stimulating the photodegradation process in the absence than in the presence the flavin cofaggor (FMN). 

With respect to C-parathion and Cl-toxaphene, protease-liberated flavoprotein was significantly more active than phosphate buffer in photodegrading these chemicals to ater-soluble products (Tables II and III). The amount of C-water-soluble products formed from parathion was 5-7 times greater in the presence than in the absence of flavoprotein. It should be noted that the presence of FMN in the mixture caused a slight grange in amount of water-soluble products formed (Table II). 

Table 14.2. Proposed functions of rubrerythrin, rubredoxin oxidoreductase, rubredoxin, high molecular weight rubredoxin, and type A flavoprotein in different bacteria.

The molecular weight of these proteins ranges from 14,000 to 23,000 as shown in Table 2. Organisms which have been reported to produce flavoproteins include several species of bacteria and alga. However, unlike the case with ferredoxins, these proteins have not yet been found in higher plants and animals. 

Table 3.2.5 Disorders detectable by the in vitro probe assay. ETF Electron transfer flavoprotein, MADD multiple acyl-CoA dehydrogenase deficiency...

Table 1. Some Highlights of the Developments in the Field of Flavins and Flavoproteins...

Table 2. Flavoproteins Containing a Covalently Bound Prosthetic Group ...

The flavoproteins known to contain covalently-found prosthetic groups are listed in Table 2. In addition to the flavoproteins also carcosine oxidase from Corynebacterium contains a covalently-bound FAD Its mode of linkage is not yet known. Furthermore it seems to be the first enzyme reported to contain equivalent amounts of covalently-bound and dissociable FAD. Djmehtlyglycine dehydrogenase prossesses also a covalently linked prosthetic group, which structure is probably identical with that of (2)... 

TABLE 13-9 Some Enzymes (Flavoproteins) That Employ Ravin Nucleotide Coenzymes... 

The functions of flavoprotein enzymes are numerous and diversified.151-1533 A few of them are shown in Table 15-2 and are classified there as follows (A) oxidation of hemiacetals to lactones, (B) oxidation of alcohols to aldehydes or ketones, (C) oxidation of amines to imines, (D) oxidation of carbonyl compounds or carboxylic acids to a,(3-unsaturated compounds,... 

The reaction catalyzed by the first of these is illustrated in Table 15-2 (reaction type F). The other two enzymes usually promote the reverse type of reaction, the reduction of a disulfide to two SH groups by NADPH (Eq. 15-22). Glutathione reductase splits its substrate into two halves while reduction of the small 12-kDa protein thioredoxin (Box 15-C) simply opens a loop in its peptide chain. The reduction of lipoic acid opens the small disulfide-containing 5-membered ring in that molecule. Each of these flavoproteins also contains within its structure a reducible disulfide group that participates in catalysis. 

However, these experiments may not have established a mechanism for natural flavoprotein catalysis because the properties of 5-deazaflavins resemble those of NAD+ more than of flavins.239 Their oxidation-reduction potentials are low, they do not form stable free radicals, and their reduced forms don t react readily with 02. Nevertheless, for an acyl-CoA dehydrogenase the rate of reaction of the deazaflavin is almost as fast as that of natural FAD.238 For these enzymes a hydride ion transfer from the (3 CH (reaction type D of Table 15-1) is made easy by removal of the a-H of the acyl-CoA to form an enolate anion intermediate. 

The development by Chance of a dual wavelength spectrophotometer permitted easy observation of the state of oxidation or reduction of a given carrier within mitochondria.60 This technique, together with the study of specific inhibitors (some of which are indicated in Fig. 18-5 and Table 18-4), allowed some electron transport sequences to be assigned. For example, blockage with rotenone and amytal prevented reduction of the cytochrome system by NADH but allowed reduction by succinate and by other substrates having their own flavoprotein components in the chain. Artificial electron acceptors, some of which are shown in Table 18-5,... 

The lipid-soluble ubiquinone (Q) is present in both bacterial and mitochondrial membranes in relatively large amounts compared to other electron carriers (Table 18-2). It seems to be located at a point of convergence of the NADH, succinate, glycerol phosphate, and choline branches of the electron transport chain. Ubiquinone plays a role somewhat like that of NADH, which carries electrons between dehydrogenases in the cytoplasm and from soluble dehydrogenases in the aqueous mitochondrial matrix to flavoproteins embedded in the membrane. Ubiquinone transfers electrons plus protons between proteins within the... 

The other classes of flavoproteins in table 10.2 interact with molecular oxygen either as the electron-acceptor substrates in redox reactions catalyzed by oxidases or as the substrate sources of oxygen atoms for oxygenases. Molecular oxygen also serves as an electron acceptor and source of oxygen for metalloflavoproteins and dioxygenases, which are not listed in the table. These enzymes catalyze more complex reactions, involving catalytic redox components, such as metal ions and metal-sulfur clusters in addition to flavin coenzymes. 

A recurrent theme in many flavoprotein reactions is the probable involvement of FADH2 or the reduced form of FMN (FMNH2) as transient intermediates. Figure 10.10 illustrates a reasonable catalytic pathway for the first enzyme listed in table 10.2 this reaction shows the likely involvement of E FADH2 in each case. The mechanisms by which E FAD is reduced to E FADH2 by NADPH in the for-... 

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