PURIFICATION AND CHARACTERIZATION OF A MALTOTETRAOSE-FORMING ALKALINE ALPHA-AMYLASE FROM AN ALKALOPHILIC BACILLUS STRAIN, GM8901

Abstract

An alkalophilic bacterium, Bacillus sp. strain GM8901, grown at pH 10.5 and 50 degrees C, produced five alkaline amylases in culture broth. At an early stage of the bacterial growth, amylase I (Amyl I) was produced initially and then, as cultivation progressed, four alkaline amylases, Amyl II, Amyl III, Amyl IV, and Amyl V, were produced from proteolytic degradation of Amyl I. A serine protease present in the culture medium was believed to be involved in Amyl I degradation, We purified Amyl I from the culture supernatant by ammonium sulfate precipitation, heparin-Sepharose CL-6B column chromatography, phenyl-Toyopearl column chromatography, and Mono Q HR5/5 high-performance liquid chromatography. The molecular weight of Amyl I was estimated to be about 97,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Amyl I had an extremely high optimal pH of 11.0 to 12.0 and was stable in a broad pH range of 6.0 to 13.0. Amyl I had an optimal temperature of 60 degrees C and was stable up to 50 degrees C. Thermostability was increased in the presence of Ca2+ and soluble starch. The enzyme required metal ions such as Ca2+, Mg2+, Cu2+, Co2+, Ag+, Zn2+, and Fe2+ for its enzyme activity and was inhibited by 1 mM EDTA and 1 mM phenylmethylsulfonyl fluoride. According to the mode of action of Amyl I on starch, Amyl I was classified as an alpha- and exo-amylase. Amyl I produced maltotetraose predominantly from starch via intermediates such as maltohexaose and maltopentaose.