Properties of novel thermostable glucoamylase from the hyperthermophilic archaea, Sulfolobus solfataricus, in relation to glucose production

Abstract

The properties of a putative glucoamylase from a hyperthermophilic archaea, Sulfolobus solfataricus (SSG), were examined in relation to the process of glucose syrup. The recombinant glucoamylase was extremely thermostable showing its optimal temperature at 90°C. In addition, the enzyme was most active in the pH range of 5.5 ? 6.0. In particular, substrate preference toward maltotriose distinguished this enzyme from other fungal glucoamylase. The isomaltose formation by reverse reaction was significantly reduced when compared to that of industrial fungal glucoamylase (AMG) and the glucose yield was about 96%. To reduce the reverse reaction of the enzyme, serine at the position 600 was replaced with alanine by site-directed mutagenesis. S600A reduced the isomaltose formation by reverse reaction compared with the wild type enzyme.Then, the glucoamylase from Sulfolobus solfataricus and its mutant enzyme S600A acting at pH 6.0 and high temperature provides the excellent properties for improved industrial starch process by eliminating the adjusting step of both pH and temperature.