Application of Zinc Hydroxide in the Purification of Bean Alpha-Amylase Inhibitor

A novel step in bean (Phaseolus vulgaris) alpha-amylase inhibitor (AAI) purification, based on the application of an inorganic adsorbent, zinc hydroxide, was developed. The new method was substantially faster than existing protocols. Up to 98% of bean seed proteins were bound to the white precipitate in the range of 1-4% (w/v) zinc hydroxide, while the amount of bound bean AAI was far less in the range of 1-2%. The AAI-enriched fraction, unbound by zinc hydroxide, was further purified by DEAE-(diethylaminoethyl)chromatography and gel filtration. It was found that zinc hydroxide binds the majority of soluble proteins of bean, while it leaves alpha-amylase inhibitor in solution. The binding of proteins to zinc-hydroxide occurs in a short time and the change caused in the buffer composition is insignificant, thus it may open new approaches in purification of other proteins, too.