<p>This domain is found in a number of proteins including flavodoxin and nitric-oxide synthase. Flavodoxins are electron-transfer proteins that function in various electron transport systems. They bind one FMN molecule, which serves as aredox-active prosthetic group [<cite idref="PUB00000480"/>] and are functionally interchangeable with ferredoxins. They have been isolated from prokaryotes, cyanobacteria, and some eukaryotic algae. Nitric oxide synthase (<db_xref db="EC" dbkey="1.14.13.39"/>) produces nitric oxide from L-arginie and NADPH. Nitric oxide acts as a messenger molecule in the body.</p>