On the Structure and Function of Reduced Nicotinamide Adenine Dinucleotide Phosphate‐Cytochrome f Reductase of Spinach Chloroplasts

Abstract

NADPH‐eytochrome f reductase from spinach chloroplasts has been purified, and its amino acid composition is reported. The specificity of the enzyme for different electron acceptors has been studied. In addition to higher plant cytochrome f, Euglena gracilis cytochrome f and plastocyanin are reduced. The reaction with these acceptors occurs through a two‐step mechanism, whereas higher plant cytochrome f forms a ternary complex with NADPH and the enzyme. The Km values for NADPH in the reactions with the different electron acceptors, the Km's for the electron acceptors and the turnover numbers are reported. The sulphydryl reagents slowly inactivate the enzyme and enhance the fluorescence of enzyme‐bound FAD and of the tryptophan residues of the protein. In the presence of NADPH, the inactivation is very rapid, and FADH2 is split from the apoenzyme. Preincubation of the enzyme with NADPH inactivates reversibly all the reactions except cytochrome f reductase.The results are interpreted in terms of structure to function relationships and the significance of the NADPH‐cytochrome f reductase in photosynthetic electron transport is also discussed.

Purification and Characterization of a Ferredoxin-NADP+ Oxidoreductase-Like Enzyme from Radish Root Tissues

“…With regard to the root FNR-like enzyme, the effect of NaCl concentration on activity was consistent with that observed for other FNRs. When MgCl2 was used instead of NaCl, the decrease of activity was observed at (8,16). As described in purification steps, this enzyme had a stronger affinity to cibacron-blue dye than to ferredoxin, judging from the NaCl concentration required for elution from Blue-Cellulofine and Ferredoxin-Sepharose 4B.…”

Association of ferredoxin‐NADP+ oxidoreductase with the chloroplast cytochrome b‐f complex

“…Ferredoxin-NADP+ oxidoreductase (FNR) was isolated from spinach as described in section 2. Values from [14] are shown for comparison for amino acid analysis. Table 1 compares the amino acid composition of the 37-kDa polypeptide with that of isolated ferredoxin-NADP+ oxidoreductase and with literature values [ 141 for this enzyme.…”

The TP0796 Lipoprotein of Treponema pallidum Is a Bimetal-dependent FAD Pyrophosphatase with a Potential Role in Flavin Homeostasis

“…The assay for FAD pyrophosphatase (EC 3.6.1.18) activity was adapted from the method of Forti and Sturani (32). It exploits the fact that fluorescence of FMN is higher than that of an FAD solution of the same concentration and that pyrophosphatase catalyzes the conversion of FAD to FMN and AMP.…”