Thioredoxin Reductase-Type Ferredoxin: NADP⁺ Oxidoreductase of <i>Rhodopseudomonas palustris</i>: Potentiometric Characteristics and Reactions with Nonphysiological Oxidants

• Main Authors: Mindaugas Lesanavičius (Author), Daisuke Seo (Author), Narimantas Čėnas (Author)
• Format: Book
• Published: MDPI AG, 2022-05-01T00:00:00Z.
• Subjects: article
• Online Access: Connect to this object online.
• Notes: 10.3390/antiox11051000; 2076-3921
• Keywords: <i>Rhodopseudomonas palustris</i>; ferredoxin:NADP⁺ oxidoreductase; thioredoxin reductase; quinones; nitroaromatic compounds; reduction mechanism; Therapeutics. Pharmacology; RM1-950
• Source: Antioxidants, Vol 11, Iss 5, p 1000 (2022)

<i>Rhodopseudomonas palustris</i> ferredoxin:NADP⁺ oxidoreductase (<i>Rp</i>FNR) belongs to a novel group of thioredoxin reductase-type FNRs with partly characterized redox properties. Based on the reactions of <i>Rp</i>FNR with the 3-acetylpyridine adenine dinucleotide phosphate redox couple, we estimated the two-electron reduction midpoint potential of the FAD cofactor to be −0.285 V. 5-Deaza-FMN-sensitized photoreduction revealed −0.017 V separation of the redox potentials between the first and second electron transfer events. We examined the mechanism of oxidation of <i>Rp</i>FNR by several different groups of nonphysiological electron acceptors. The <i>k</i>_cat/<i>K</i>_m values of quinones and aromatic <i>N</i>-oxides toward <i>Rp</i>FNR increase with their single-electron reduction midpoint potential. The lower reactivity, mirroring their lower electron self-exchange rate, is also seen to have a similar trend for nitroaromatic compounds. A mixed single- and two-electron reduction was characteristic of quinones, with single-electron reduction accounting for 54% of the electron flux, whereas nitroaromatics were reduced exclusively via single-electron reduction. It is highly possible that the FADH· to FAD oxidation reaction is the rate-limiting step during the reoxidation of reduced FAD. The calculated electron transfer distances in the reaction with quinones and nitroaromatics were close to those of <i>Anabaena</i> and <i>Plasmodium falciparum</i> FNRs, thus demonstrating their similar "intrinsic" reactivity.