Purification and Characterization of Six Kiwifruit Proteases Isolated with Two Ion-exchange Resins, Toyopearl-SuperQ and Bakerbond WP-PEI

Abstract

Kiwifruit (Actinidia chinensis) contains a cysteine protease, actinidin, and it was suggested to contain two components, A1 and A2. However, the separation of two components was not shown, and the comparison of the two components has not been thoroughly done. We have now shown that actinidin can be separated into six proteases, named KP1, KP2, KP3, KP4, KP5, and KP6, by improved polyacrylamide gel electrophoresis at pH 4.0. Each kiwifruit protease was purified with two ion-exchange resins, Toyopearl-SuperQ and Bakerbond WP-PEI. Before the purification of kiwifruit proteases, excess p-chloromercuribenzoate was added to crude kiwifruit protease to prevent the autodigestion. Each kiwifruit protease had a molecular mass of 23, 500 and the same amino terminal sequences from the first to the thirteenth. They had different pI's. These six kiwifruit proteases were divided into two groups by the effects of DTT and Zn²⁺ on the activity. These results indicated that the six components must be A1, A2, and four previously unknown proteases. Thus we have separated the kiwifruit proteases which were thought to be two, into six components.