Trypsin inhibitors from Colocasia esculenta, Alocasia macrorrhiza and Cyrtosperma chamissonis

Abstract

Trypsin inhibitors from three edible aroids of the family Araceae, viz. taro ( Colocasia esculenta) var. esculenta) giant taro ( Alocasia macrorrhiza) and giant swamp taro ( Cyrtosperma chamissonis) obtained from the Pacific region, were isolated by affinity chromatography and purified by gel filtration. The M r of these inhibitors, as determined by gel filtration were 35 000–38 000, but were ca 20 000 by SDS gradient PAGE. A time course of heating in SDS showed a ready dissociation of the native protein into subunits of equal size. Further experiments showed that there were no disulfide bonds between these subunits. A single N-terminal sequence was found for each inhibitor showing that the two subunits had similar primary structure. Each of the N-terminal sequences showed homology with that of soybean trypsin inhibitor. To our knowledge, this finding follows only one other example of a Kunitz family inhibitor being located in a monocotyledonous, rather than dicotyledonous, plant species, and indicates that the ancestral gene from which Kunitz family inhibitors originate predates the evolutionary divergence of flowering plants into monocotyledons and dicotyledons.