Flavocytochrome

Yeast mitochondrial flavocytochrome 2 (lactate cytochrome c oxido-reductase) catalyzes the transfer of electrons from L-lactate to various acceptors, cytochrome c being the physiological acceptor. The protoheme and flavin mononucleotide, because of their higher redox potential, can both be reduced completely by L-lactate the enzyme accepts a total of three electrons per protomer, which amounts to twelve electrons for the stable active tetramer. Both types of prosthetic group are quantitatively reoxidized by external acceptors. 

Combined stopped-flow and rapid-freezing ESR techniques show that on binding of L-lactate to each protomer, two electrons are transferred from this bound substrate to the flavin, which becomes fully reduced hydro-quinone (Campeillere-Blandin, 1975). In step 2, one of the electrons is 

Tungsten-containing sulfite oxidase is present in the livers of rats 

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L-lactate-cytochrome c-oxidoreductase (flavocytochrome was isolated for the first time from the thermo-tolerant yeast H. polymorpha. The mentioned above enzyme preparations were used for construction of the biorecognition elements of electrochemical sensors. 

On the base of alcohol oxidase and flavocytochrome b, the enzymatic kits for selective assay of ethanol, methanol, formaldehyde and L-lactate were developed. 

Natural and semisynthetic monocomponent flavocytochromes as catalytically self-sufficient monooxygenases 97MI19. 

The oxidation by strains of Pseudomonas putida of the methyl group in arenes containing a hydroxyl group in the para position is, however, carried out by a different mechanism. The initial step is dehydrogenation to a quinone methide followed by hydration (hydroxylation) to the benzyl alcohol (Hopper 1976) (Figure 3.7). The reaction with 4-ethylphenol is partially stereospecific (Mclntire et al. 1984), and the enzymes that catalyze the first two steps are flavocytochromes (Mclntire et al. 1985). The role of formal hydroxylation in the degradation of azaarenes is discussed in the section on oxidoreductases (hydroxylases). 

Reeve CD, MA Carver, DJ Hopper (1989) The purification and characterization of 4-ethylphenol methylene hydroxylase, a flavocytochrome from Pseudomonas putida JDl. Biochem J 263 431-437. 

A first application using ferroceneboronic acid as mediator [45] was described for the transformation of p-hydroxy toluene to p-hydroxy benzaldehyde which is catalyzed by the enzyme p-cresolmethyl hydroxylase (PCMH) from Pseudomonas putida. This enzyme is a flavocytochrome containing two FAD and two cytochrome c prosthetic groups. To develop a continuous process using ultrafiltration membranes to retain the enzyme and the mediator, water soluble polymer-bound ferrocenes [50] such as compounds 3-7 have been applied as redox catalysts for the application in batch electrolyses (Fig. 12) or in combination with an electrochemical enzyme membrane reactor (Fig. 13) [46, 50] with excellent results. 

The success of Chapman and co-workers in expression of flavocytochrome 2 in E. coli [23] is encouraging in its impUcations for future expression of flavoproteins in this host because, in their experience both the flavin and heme groups are incorporated into the recombinant protein. Moreover, the bacterial expression system produces the protein 500-1000 fold more efficiently than the yeast from which it was cloned. The enzyme produced in E. coli, however, lacks the first five amino acid residues at its amino terminus, a result which presumably reflects subtle differences in protein synthesis between the two organisms. 

Since the primary structure of a peptide determines the global fold of any protein, the amino acid sequence of a heme protein not only provides the ligands, but also establishes the heme environmental factors such as solvent and ion accessibility and local dielectric. The prevalent secondary structure element found in heme protein architectures is the a-helix however, it should be noted that p-sheet heme proteins are also known, such as the nitrophorin from Rhodnius prolixus (71) and flavocytochrome cellobiose dehydrogenase from Phanerochaete chrys-osporium (72). However, for the purpose of this review, we focus on the structures of cytochromes 6562 (73) and c (74) shown in Fig. 2, which are four-a-helix bundle protein architectures and lend themselves as resource structures for the development of de novo designs. 

Fig. 11. Molecular model and electron transfer kinetics of the flavocytochrome ma-quette containing two bis-histidine hgated hemes and two covalently bound flavins (149). Copyright 1998 National Academy of Sciences, USA.

Cinnamaldehyde complexes with iron, 12 246 Circular dichroism flavocytochrome b, 36 271 magnetic, see Magnetic circular dichroism Rieske and Rieske-type proteins, 47 113, 115-116... 

Electronic absorption spectroscopy charge transfer transitions, 19 71 d-d transitions, 19 70, 71 flavocytochrome b, 36 269-271 intraligand transitions, 19 71-80 of organometallics, 19 69-80 Electronic coupling, between donor and acceptor wave functions, 41 278 Electronic nuclear double resonance spectroscopy, molybdenum center probes, 40 13... 

Electron transfer (continued) intramolecular, from type-1 copper center to trinuclear copper center blue copper oxidases, 40 175-178 iron-sulfur proteins, 47 405, 474-479 kinetic model, flavocytochrome bj, 36 282-283... 

P-cluster pair role, 40 108-111 physiological pathway, flavocytochrome f 2> 36 275-276... 

Flavin mononucleotide, 3absorption coefficients, 36 270 active site, 36 265-267 catalysis and electron transfer, 36 275-287 carbanion mechanism, 36 277-282 electron acceptors, 36 285-287 electron transfer pathway, 36 275-276, 282-285... 

Tyr 143, 36 293 Tyr 254, 36 291-293 NMR spectroscopy, 36 271-272 pH dependence, 36 274-275 primary stmcture, 36 261-263 prosthetic groups structure, 36 258 quaternary structure, 36 261-262 reduction potentials, 36 268-269 short electron transport chain, 36 258-259 site-directed mutagenesis, 36 289-290 substrate specificity, 36 272-274 Flavocytochrome C552 electrochemistry, 36 365-367, 369... 

Hammett s-constants, of astatophenols, 31 66 Hansenula anomala, flavocytochrome bj from, 36 260-261... 

Muonium chemistry gaseous phase, 28 119-120 liquid mixtures, 28 120-122 radical formation and reactions, 28 122-130 Mushrooms, vanadium in, 35 96-97 Mutagenesis, site-directed, flavocytochrome bj, 36 289-290 MXj-... 

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