Complex formation of a 4-alpha-glucanotransferase using starch as a biocatalyst for starch modification

Abstract

A 4-alpha-glucanotransferases from Thermus thermophilus (TT alpha GT) possesses an extra substrate binding site, leading to facile purification of the intact enzyme using amylose as an insoluble binding matrix. Due to the cost of amylose and low recovery yield, starch was replaced for amylose as an alternative capturer in this study. Using gelatinized corn starch at pH 9 with 36-h incubation in the presence of 1 M ammonium sulfate increased the TT alpha GT-starch complex formation yield from 2 to 56%. In preparative-scale production, TT alpha GT produced in Bacillus subtilis was recovered by 42.1% with the same specific activity as that of purified TT alpha GT. Structural and rheological analyses of the enzymatically modified starches revealed that the starch complex exhibited catalytic performance comparable to soluble TT alpha GT, suggesting that the starch complex can be used as a biocatalyst for modified starch production without elution of the enzyme from the complex.