Chloroplast ferredoxin-NADP؉ reductase has a 32,000-fold preference for NADPH over NADH, consistent with its main physiological role of NADP ؉ photoreduction for de novo carbohydrate biosynthesis. Although it is distant from the 2-phosphoryl group of NADP ؉ , replacement of the C-terminal tyrosine (Tyr 308 in the pea enzyme) by Trp, Phe, Gly, and Ser produced enzyme forms in which the preference for NADPH over NADH was decreased about 2-, 10-, 300-, and 400-fold, respectively. Remarkably, in the case of the Y308S mutant, the k cat value for the NADH-dependent activity approached that of the NADPH-dependent activity of the wild-type enzyme. Furthermore, difference spectra of the NAD ؉ complexes revealed that the nicotinamide ring of NAD ؉ binds at nearly full occupancy in the active site of both the Y308G and Y308S mutants. These results correlate well with the k cat values obtained with these mutants in the NADH-ferricyanide reaction. The data presented support the hypothesis that specific recognition of the 2-phosphate group of NADP(H) is required but not sufficient to ensure a high degree of discrimination against NAD(H) in ferredoxin-NADP ؉ reductase. Thus, the C-terminal tyrosine enhances the specificity of the reductase for NADP(H) by destabilizing the interaction of a moiety common to both coenzymes, i.e. the nicotinamide.

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Although all ferredoxin-NADP+ reductases (FNRs) catalyze the same reaction. i. e. the transfer of reducing equivalents between NADP(H) and ferredoxin, they belong to two unrelated families of proteins: the plant type and the glutathione reductase type of FNRs. Aim of this review is to provide a general classification scheme for these enzymes, to be used as a framework for the comparison of their properties.Furthermore, we report on some recent findings, which significantly increased the understanding of the structure-function relationships of FNRs, i.e. the ability of adrenodoxin reductase and its homologs to catalyze the oxidation of NADP+ to its 4-oxo derivative, and the properties of plant-type FNRs from non- Subject: revision of ms ABBI-07-950Dear Editor, we would like to thank the Reviewers for their criticisms and suggestions that hopefully allowed us to improve our article. We carefully revised the manuscript according to the Reviewer's suggestions. The overall length of the paper has been significantly reduced by shortening longer chapters and by deleting three figures.The major changes in the revised version of the manuscript are as follows: Fig. 1, GR-type FNRs represent a broader group that include both the AdR-like and the ONFR-like enzymes. Thus, we prefer to maintain the distinction between the two terms (GR-type and AdR-like).2) While most of the chapters have similar lengths, the last two chapters are significantly longer than the previous six ones, creating an unpleasant imbalance in the presentation. The authors should try to either condense or split in multiple chapters the two long ones, in order to have a more armonious and balanced presentation of the topics. Large chapters ("Specific features of Plasmodium falciparum FNR" and "Ferredoxin binding and electron-transfer") were significantly shortened (by 35% and 22%, respectively). Previous very long paragraphs were broken into smaller ones.3) The work would significantly gain in strength upon adding a small summary paragraph at the end of the review article. Alternatively, the authors may consider a paragraph in which they present open questions that can now be raised and answered based upon current knowledge. A Conclusion chapter has been added. However, in order to limit the ms length, this chapter is not a summary or a list of open questions, but includes just some concluding remarks. 5) A list of abbreviations should be included. For example, what is NMN?A list of abbreviations has been added. 6) On page 4 line 15, both n and S should be defined.The definition of the parameters n and S has been given, and a reference added. 7) The authors should specify clearly which enzymes have been wrongly identified as adrenodoxin reductase-like enzymes (page 6).What we found is that some AdR-like proteins have been wrongly identified as other enzymes, and not the opposite. We think that, for the sake of brevity, it is not possible to give a comprehensive list of incorrectly identified entries within this review article. We have provide...

Renalase is a recently discovered flavoprotein that regulates blood pressure, regulates sodium and phosphate excretion, and displays cardioprotectant action through a mechanism that is barely understood to date. It has been proposed to act as a catecholamine-degrading enzyme, via either O(2)-dependent or NADH-dependent mechanisms. Here we report the renalase crystal structure at 2.5 Å resolution together with new data on its interaction with nicotinamide dinucleotides. Renalase adopts the p-hydroxybenzoate hydroxylase fold topology, comprising a Rossmann-fold-based flavin adenine dinucleotide (FAD)-binding domain and a putative substrate-binding domain, the latter of which contains a five-stranded anti-parallel β-sheet. A large cavity (228 Å(3)), facing the flavin ring, presumably represents the active site. Compared to monoamine oxidase or polyamine oxidase, the renalase active site is fully solvent exposed and lacks an 'aromatic cage' for binding the substrate amino group. Renalase has an extremely low diaphorase activity, displaying lower k(cat) but higher k(cat)/K(m) for NADH compared to NADPH. Moreover, its FAD prosthetic group becomes slowly reduced when it is incubated with NADPH under anaerobiosis, and binds NAD(+) or NADP(+) with K(d) values of ca 2 mM. The absence of a recognizable NADP-binding site in the protein structure and its poor affinity for, and poor reactivity towards, NADH and NADPH suggest that these are not physiological ligands of renalase. Although our study does not answer the question on the catalytic activity of renalase, it provides a firm framework for testing hypotheses on the molecular mechanism of its action.

The crystal structure of ferredoxin-NADP+ reductase (FNR) suggests that Ser96 is directly involved in hydride transfer between the isoalloxazine moiety of FAD and the nicotinamide ring of NADP(H). To probe its role, Ser96 has been mutated to valine (S96V) and glycine (S96G). These mutations primarily affected the interaction of the nicotinamide ring with the flavin. Absorbance, fluorescence, and circular dichroism spectra and the crystal structure of FNR-S96V indicate that this mutant folds properly. FNR-S96V shows only 0.05% of wild-type activity, while the affinities for both ferredoxin and NADP+ are virtually unchanged. However, spectral perturbations induced by NADP+ binding to FNR-S96V strongly resemble those elicited by the binding of 2'-monophosphoadenosine-5'-diphosphoribose, a substrate analog lacking the nicotinamide ring, both to the mutant and wild-type enzymes. Rapid reaction studies on the valine mutant failed to detect charge-transfer intermediates during flavin reduction by NADPH. In addition, no semiquinone formation was seen during photoreduction of FNR-S96V. The three-dimensional structure of the valine mutant shows small, albeit definite, changes only in the isoalloxazine microenvironment. The glycine mutant of FNR displays behavior intermediate between that of wild-type enzyme and that of the valine mutant. It maintains ca. 2% of the wild-type activity as well as the ability to form the charge-transfer species between reduced FNR and NADP+. In photoreduction experiments, the same degree of flavin semiquinone stabilization was observed with FNR-S96G and with the wild-type enzyme. NADP+ binding to the glycine mutant was very similar to that observed in the case of the valine mutant.(ABSTRACT TRUNCATED AT 250 WORDS)