Proteinases are enzymes that catalyse the breakdown of proteins. Proteinases are involved in many biological functions, including the digestion of ingested proteins, the breakdown of old proteins, and cell signalling. They also facilitate the formation of new protein products.

Low concentrations of Proteinase caused a small amount of dimerization of alpha 1I3, but no difference in inhibition or receptor binding was detected between purified dimers or monomers. Kininogen domains of 22 and 64 kDa were allowed to react with alpha 1I3- or alpha 2M-bound papain to probe the accessibility of the active site of this Proteinase.[1]