ferredoksinNADPreduktase

Ferredoxin-NAD+ reductase, also known as FNR, is a key enzyme in the electron transport chain of many organisms, particularly bacteria and chloroplasts. It plays a crucial role in ferredoxin metabolism, acting as a bridge between the reduced ferredoxin pool and NAD+ reduction. The enzyme facilitates the transfer of electrons from reduced ferredoxin to NAD+, generating NADH. This process is vital for cellular energy production and various reductive biosynthesis pathways.

The reaction catalyzed by FNR is typically represented as: 2 reduced ferredoxin + NAD+ + H+ → 2 oxidized ferredoxin + NADH. The enzyme utilizes a flavin cofactor, usually flavin mononucleotide (FMN) or flavin adenine dinucleotide (FAD), to mediate the electron transfer. FNR is a homodimer, with each subunit containing a binding site for ferredoxin and the flavin cofactor. Its structure allows for efficient interaction with its substrates, ensuring rapid electron flow.

In photosynthetic organisms, FNR is located in the chloroplast stroma and links the light-dependent reactions of photosynthesis to the Calvin cycle. It reduces NADP+ to NADPH, which is then used as a reducing agent in carbon fixation. In anaerobic bacteria, FNR is involved in various metabolic pathways, including nitrogen fixation and sulfur reduction, where it provides reducing power. The enzyme's versatility and essential role in electron transfer make it a central component of redox homeostasis in diverse biological systems.