ferroredoxinNADP

Ferredoxin-NADP+ reductase, often abbreviated as FNR, is a flavoprotein enzyme found in the stroma of chloroplasts and in some bacteria. Its primary function is to catalyze the final step of electron transfer in the photosynthetic electron transport chain. Specifically, FNR accepts electrons from ferredoxin, a small iron-sulfur protein, and transfers them to NADP+. This reaction produces NADPH, a crucial reducing agent used in the Calvin cycle for carbon fixation and in other biosynthetic pathways. The enzyme's structure is a homodimer, with each monomer containing a flavin adenine dinucleotide (FAD) prosthetic group. FNR is also involved in other metabolic processes, including nitrogen assimilation and sulfur reduction, depending on the organism. In some cyanobacteria and plants, FNR can also participate in light-dependent NADPH production independent of carbon fixation. The regulation of FNR activity is complex, influenced by light, the redox state of the cell, and the availability of its substrates. It is an essential enzyme for maintaining redox homeostasis and enabling anabolic processes in photosynthetic organisms.