Ferredoxin-NADP+reductase

5 Ferredoxin-NADP Reductase. - Photosynthetic reduction of NADP+ to NADPH in cyanobacteria and higher plants involves electron transfer from photosystem I to an 11 kDa, [2Fe-2S] containing soluble ferredoxin that is 

---

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 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. 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... 

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... 

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].

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... 

Boger m) showed that the transhydrogenase activity catalyzed by ferredoxin-NADP reductase obtained from Bumilleriopsis filiformis, which is very similar to the spinach enzyme, is regulated by ferredoxin and that one common nicotinamide nucleotide binding site is involved in both the diaphorase and the transhydrogenase reactions. 

Ferredoxin has been shown to interact with the thylakoids at two distinct sites [51] it accepts electrons from the reducing side of PS I, then is reoxidized by the thylakoid-bound FAD-flavoprotein, ferredoxin-NADP reductase (FNR) [50]. It has been shown that FNR forms a one-to-one complex with Fd when the two proteins are in solution [52] as well as when FNR is membrane-bound [53], with a disso-... 

In all oxygen-evolving organisms, the PS I reaction centres finally reduce a water-soluble ferredoxin. This small protein of around 10 kDa has a (2Fe-2S) cluster and a rather low midpoint reduction potential of -400 mV. Ferredoxin binds to the PS I centre after reduction it participates both in linear electron flow to NADP, via ferredoxin-NADP reductase, and in cyclic electron flow around the PS I centre. Two membrane-bound iron-sulfur centres, designated Centre A (or F, ) and Centre B (or Fg), appear to be the terminal acceptors in the reaction centre. Their mode of functioning is not clearly established and their structure is not well known, mainly because they cannot be extracted without their complete denaturation. F and Fq can be photoreduced at low temperature in cells or in purified PS I centres. Characteristic EPR spectra are thus obtained with g values of 1.86, 1.94, 2.05 for F, and 1.89, 1.92, 2.05 for F -. 

Although it was originally suggested that plastocyanin was located in the lumen, contradictory reports followed. However, studies with vesicles of opposite sidedness verified that plastocyanin was indeed bound to the inner thylakoid surface [39], consistent with its function in the lumen [6]. The final PS I electron acceptors, ferredoxin and ferredoxin-NADP reductase, are located on the stroma-facing side of the thylakoid membrane [40]. 

Additional polypeptides ascribed to the Cyt b-f complex are a bound form of ferredoxin-NADP reductase (FNR) [99] and one or more smaller polypeptides [100]. An association of the complex with ferredoxin-NADP reductase may be expected in view of the reported role of FNR in cyclic electron flow from PS I to the Cyt complex [101]. FNR remains associated with the complex during the early stages of the purification of the complex but there is no evidence that it is an intrinsic component of the complex necessary for plastoquinol-plastocyanin oxido-reductase. The presence of small polypeptides in the complex requires further investigation. Polypeptides of about 5 kDa have been reported to be associated with the spinach complex [100]. 

---