The proteolytic enzyme mucunain (cysteine protease) is a protein found in the tissue of certain legumes of the genus Mucuna, especially the velvet bean(Mucuna pruriens). Mucuna pruriens is used naturopathically in Parkinson's disease.
In Mucuna pruriens (velvet bean, a tropical legume), mucunain occurs in the hairs covering the seed pods (Singh SK et al. 2018). When these come into contact with the skin, they release mucunain. Mucunain is a ligand for protease-activated receptors 2 and 4 (Reddy VB et al. 2008). It causes intense itching in the skin without accompanying erythema, as occurs, for example, with histamine.