Cyclic α-1,4-glucan formation by bacterial α-amylases

Abstract

Cyclic α-1,4-glucan formation from synthetic amylose by hydroquinone glucosylating enzyme (HGE), which is a saccharifying α-amylase, was investigated. Upon analysis of reaction products from synthetic amylose, glucans which were not hydrolyzed by glucoamylase were detected with HPAEC in reaction mixtures. The glucans were hydrolyzed by HGE to maltooligosaccharides and hydrolyzed to glucose by the combination of HGE and glucoamylase. From these results, these glucans might be considered to be cyclic α-1,4-glucans. In order to demonstrate that these glucans were cyclic α-1,4-glucans, phenol-sulfate test, Somogyi-Nelson test, and tritium labeling test of reducing ends were conducted. From results of these tests, it was confirmed that these compounds were saccharides and did not have reducing ends. Furthermore, the molecular weight of each glucan was determined using TOF-MS spectrometry. Each molecular weight agreed with that of cyclic glucans theoretically calculated. One of these glucans was purified and was identified to be γ-cyclodextrin. These results demonstrate that HGE formed cyclic α-1,4-glucans. Cyclic α-1,4-glucans were also detected in the reaction mixtures of bacterial saccharifying α-amylase and bacterial liquefying α-amylase.