Ferredoxin-NADP

The immediate electron acceptor for P700 is a special molecule of chlorophyll. This unique Chi a (Aq) rapidly passes the electron to a specialized quinone (Aj), which in turn passes the e to the first in a series of membrane-bound ferredoxins (Fd, Chapter 21). This Fd series ends with a soluble form of ferredoxin, Fd, which serves as the immediate electron donor to the fiavo-protein (Fp) that catalyzes NADP reduction, namely, ferredoxin NADP reductase. 

The prototype of this class of soluble ferredoxins was initially obtained from spinach chloroplasts and subsequently been shown to play a role in physiological electron shuttling between PSl and a number of redox proteins, most prominently ferredoxin-NADP-reduc-tase 13). Homologous proteins were purified from several cyanobac-... 

The third study has employed 4,6-dinitrobenzofuroxan and as metabolic systems the one-electron reductants NADPHxytochrome P450 reductase and ferredoxin NADP(+) reductase and the two-electron reductants DT-diaphorase and Enterobacter cloacae nitroreductase [239]. The compound is activated either by DT-diaphorase or nitroreductase. 

Fig. 9. Absorption spectra of several flavopro-teins compared with an action spectrum of pho-totropism (dotted line C ),39))- The spectra are arranged with respect to the position of their UV-peaks (1) succinate dehydrogenase78), (2)lipo-amide dehydrogenase179), (4) lactate oxidase111), (5) D-amino acid oxidase111), (6) flavodoxin110), (7) old yellow enzyme2), (8) ferredoxin NADP+ reductase16), (9) oxynitrilase111), (10) L-amino acid oxidase111)...

Fig. 16. Ferredoxin (Fd)/ferredoxin-NADP+-reductase (FNR) mediated enzymatic carboxylation of pyruvic acid to form malic acid catalyzed by the NADPH-dependent malic enzyme (ME)...

DIHYDROOROTATE OXIDASE DIMETHYLANILINE MONOOXYCENASE FERREDOXIN NADP REDUCTASE GLUTATHIONE REDUCTASE 0-2-HYDROXY ACID DEHYDROGENASE... 

RESONANCE RAMAN SPECTROSCOPY Ferredoxin-dependent enzymes, ADRENODOXIN BENZENE 1,2-DIOXYGENASE FERREDOXIN NADP REDUCTASE GLUTAMATE SYNTHASE HYDROGENASE... 

Onda Y, Hase T (2004) FAD assembly and thylakoid membrane binding of ferredoxin NADP oxidoreductase in chloroplasts. FEBS Lett 564 116-120... 

Pyridine nucleotide-dependent flavoenzyme catalyzed reactions are known for the external monooxygenase and the disulfide oxidoreductases However, no evidence for the direct participation of the flavin semiquinone as an intermediate in catalysis has been found in these systems. In contrast, flavin semiquinones are necessary intermediates in those pyridine nucleotide-dependent enzymes in which electron transfer from the flavin involves an obligate 1-electron acceptor such as a heme or an iron-sulfur center. Examples of such enzymes include NADPH-cytochrome P4S0 reductase, NADH-cytochrome bs reductase, ferredoxin — NADP reductase, adrenodoxin reductase as well as more complex enzymes such as the mitochondrial NADH dehydrogenase and xanthine dehydrogenase. 

The catalytic significance of this observation is not known since no deviation from a two-electron Nemst plot is observed with NADH as reductant and no kinetic studies have been done to compare the rate of the NAD -facilitated comproportionation reaction with the rate of catalytic turnover. No comparable studies on the effect of NADP on the oxidation-reduction potential of ferredoxin-NADP reductase have been, to our knowledge, published. Inasmuch as the physiological role for this enzyme is reduction of the pyridine nucleotide rather than its oxidation, the potential of the enzyme should be significantly lower than that of the pyridine nucleotide couple. Indeed, a value of —445 mV has been determined for this flavoenzyme with the driving force for its reduction being due to a decrease of 90 mV in the one-electron potential of the ferredoxin reductant. This increase... 

Another flavoprotein that makes use of both one-and two-electron transfer reactions is ferredoxin-NADP+ oxidoreductase (Eq. 15-28). Its bound FAD accepts electrons one at a time from each of the two... 

The soluble electron carriers released from the reaction centers into the cytoplasm of bacteria or into the stroma of chloroplasts are reduced single-electron carriers. Bacterial ferredoxin with two Fe4S4 clusters is formed by bacteria if enough iron is present. In its absence flavodoxin (Chapter 15), which may carry either one or two electrons, is used. In chloroplasts the carrier is the soluble chloroplast ferredoxin (Fig. 16-16,C), which contains one Fe2S2 center. Reduced ferredoxin transfers electrons to NADP+ (Eq. 15-28) via ferredoxin NADP oxidoreductase, a flavoprotein of known three-dimensional structure.367 369... 

The Z scheme. [(Mn)4 = a complex of four Mn atoms bound to the reaction center of photosystem II Yz = tyrosine side chain Phe a = pheophytin a QA and Qb = two molecules of plastoquinone Cyt b/f= cytochrome hf,f complex PC = plastocyanin Chi a = chlorophyll a Q = phylloquinone (vitamin K,) Fe-Sx, Fe-SA, and Fe-SB = iron-sulfur centers in the reaction center of photosystem I FD = ferredoxin FP = flavoprotein (ferredoxin-NADP oxidoreductase).] The sequence of electron transfer through Fe-SA and Fe-SB is not yet clear. 

Photosystem I contains three iron-sulfur clusters firmly associated with the reaction center. These are designated Fe-Sx, Fe-SA, and Fe-SB in figure 15.17. The cysteines of Fe-Sx are provided by the two main polypeptides of the reaction center, which also bind P700 and its initial electron acceptors Fe-SA and Fe-SB are on a separate polypeptide. The quinone that is reduced in photosystem I probably transfers an electron to Fe-Sx, which in turn reduces Fe-SA and Fe-SB. From here, electrons move to ferredoxin, a soluble iron-sulfur protein found in the chloroplast stroma, then to a flavoprotein (ferredoxin-NADP oxidoreductase), and finally to NADP+. 

The primary structures of at least 28 [2Fe-2S] proteins have been determined.737 Twenty-six of these have been isolated from plants or algae. The remaining two are from halobacteria, and have about 20 extra residues at the N-terminus and about five extra residues at the C-terminus in comparison with the plant-type proteins. These structural differences will account for their physiological differences. Thus, the halobacteria] ferredoxin does not form a complex with ferredoxin-NADP reductase, in contrast with plant-type [2Fe-2S] ferredoxins. 

Michalowski, C.B., Schmitt, J.M. Bohnert, H.J. (1989ft). Expression during salt stress and nucleotide sequence of cDNA for ferredoxin-NADP+ reductase from M. crystallinum. Plant Physiology 89,817-23. 

FIGURE 21. Photosystem I (PS I). P700, special pair Q, plastoquinone QH2, dihy-droplastoquinone NADP, nicotinamide adenine dinucleotide phosphate FQR, ferre-doxin-quinone reductase FNR, ferredoxin-NADP reductase Fd, ferredoxin ADP, adenosine diphosphate ATP, adenosine triphosphate. 

S Nakamura. Initiation of sulfite oxidation by spinach ferredoxin-NADP reductase and ferredoxin system a model experiment of the superoxide anion radical production by metalloflavoproteins. Biochem Biophys Res Commun 41 177-183, 1970. 

Scheme 4.104 PikC-catalyzed hydroxylation ofYC-17 to methymycin and neomethymycin in the presence of NADPH, ferredoxin and ferredoxin-NADP+ reductase [433].

Figure 2. Schematic of photoinduced electron transport and phosphorylation reactions considered to occur in chloroplast lamellae [from Moreland and Hilton (2)]. Open arrows indicate light reactions solid arrows indicate dark reactions and the narrow dashed line represents the cyclic pathway. Abbreviations used PS I, photosystem I PS II, photosystem II Y, postulated electron donor for photosystem II Q, unknown primary electron acceptor for photosystem II PQ, plastoquinones cyt b, b-type cytochromes cyt f, cytochrome f PC, plastocyanin P700, reaction center chlorophyll of photosystem I FRS, ferredoxin-reducing substance Fd, ferredoxin Fp, ferredoxin-NADP oxidoreductase FeCy, ferricyanide asc, ascorbate and DPIP, 2,6-dichloropheno-lindophenol. The numbers la, lb, 2, 3, and 4 indicate postulated sites of action by...

Vollmer M, Thomsen N, Wiek S, Seeber F (2001) Apicomplexan parasites possess distinct nuclear-encoded, but apicoplast-localized, plant-type ferredoxin-NADP(+) reductase and ferredoxin. J Biol Chem 276 5483-5490... 

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