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

A 4-α-glucanotransferases from Thermus thermophilus (TTαGT) 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 TTαGT-starch complex formation yield from 2 to 56%. In preparative-scale production, TTαGT produced in Bacillus subtilis was recovered by 42.1% with the same specific activity as that of purified TTαGT. Structural and rheological analyses of the enzymatically modified starches revealed that the starch complex exhibited catalytic performance comparable to soluble TTαGT, suggesting that the starch complex can be used as a biocatalyst for modified starch production without elution of the enzyme from the complex.