Furin is a protease of animal cells that is similar in structure to the bacterial protease subtilisin. Furin is enriched in the golgi apparatus, where it functions to cleave other proteins into their mature/active forms. Furin cleaves proteins just downstream of a basic amino acid target sequence (canonically, Arg-X-(Arg/Lys)-Arg'). In addition to processing cellular precursor proteins, furin is also utilized by a number of pathogens. For example, the envelope proteins of viruses such as HIV, influenza and dengue fever viruses must be cleaved by furin or furin-like proteases to become fully functional. Anthrax toxin, pseudomonas exotoxin and papillomaviruses must be processed by furin during their initial entry into host cells. Inhibitors of furin are under consideration as therapeutic agents for treating anthrax infection.

Furin is named after Japanese Buddhist bells used in religous ceremonies. The furinis the largest of these and supposedly prepares the mind in the same way furin prepares proteins.