Properties of amylase immobilized on a new reversibly soluble-insoluble polymer and its application to repeated hydrolysis of soluble starch.

Abstract

A copolymer of glycidyl methacrylate (GMA) and N-isopropyl acrylamide (NIPAM) forms a reversibly soluble-insoluble (S-IS) polymer (GMA-NIPAM), whose solubility changes with the temperature of the solution. An amylase (Dabiase) was immobilized on GMA-NIPAN under alkaline conditions. The specific activity of Dabiase immobilized on GMA-NIPAM (D-GN) for saccharification of soluble starch was 90% that of native Dabiase and higher than that of conventional solid immobilized enzymes. D-GN was soluble below 32°C but insoluble above 44°C. When NaCl was added to a buffer solution (pH 5.0) with D-GN, the solubility response of D-GN to change in temperature was more sensitive than that in the buffer solution without NaCl. In addition, the temperature causing half of the maximum turbidity decreased by about 2.3°C whenever the NaCl concentration of the buffer solution was increased by 1%. D-GN was used successively for repeated hydrolysis reaction of soluble starch, in which D-GN was insolubilized not only by elevating the temperature of reaction mixture with 1% NaCl from 30°C to 38°C, but also by adjusting the NaCl concentration of reaction mixture to 4% at 30°C, followed by its batchwise recovery from a reaction product by centrifugation.