Aqueous extracts of the aril of the seed of Thaumatococcus daniellii contain, in addition to the intensely sweet protein thaumatin, a cysteine protease that we have termed thaumatopain. Thaumatopain has been purified by ion-exchange chromatography from arils, and is a monomeric protein of Mr 30,000. The protease strongly resembles papain in proteolytic activity, pH optima, susceptibility to inhibitors of cysteine proteases and in N-terminal sequence. The protease has also been identified in crude aril extracts by affinity labelling with iodo[14C]acetate. Thaumatopain is responsible for the cysteine protease activity previously attributed to thaumatin. Thaumatin is digested by thaumatopain at neutral to alkaline pH values.
