title: Effects of temperature and additives on the thermal stability of glucoamylase from Aspergillus niger.
abstract: GAM-1 and GAM-2, two themostable glucoamylases from Aspergillus niger B-30, possess different molecular masses, glycosylation, and thermal stability. In the present study, the effects of additives on the thermal inactivation of GAM-1 and GAM-2 were investigated. The half-lives of GAM-1 and GAM-2 at 70°C were 45 and 216 min, respectively. Data obtained from fluorescence spectroscopy, circular dichroism spectroscopy, UV absorption spectroscopy, and dynamic light scattering demonstrated that during the thermal inactivation progress, combined with the loss of the helical structure and a majority of the tertiary structure, tryptophan residues were partially exposed and further led to glucoamylases aggregating. The thermal stability of GAM-1 and GAM-2 was largely improved in the presence of sorbitol and trehalose. Results from spectroscopy and Native-PAGE confirmed that sorbitol and trehalose maintained the native state of glucoamylases and prevented their thermal aggregation. The loss of hydrophobic bonding and helical structure was responsible for the decrease of glucoamylase activity. Additionally, sorbitol and trehalose significantly increased the substrate affinity and catalytic efficiency of the two glucoamylases. Our results display an insight into the thermal inactivation of glucoamylases and provide an important base for industrial applications of the thermally stable glucoamylases.
authors.affiliation: Key Laboratory for Molecular Enzymology and Engineering of Ministry of Education, School of Life Sciences, Jilin University, Changchun 130012, P.R. China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.forename: Zhaoli
authors.initials: Z
authors.lastname: Meng
authors.forename: Ruilin
authors.initials: R
authors.lastname: Shi
authors.forename: Le
authors.initials: L
authors.lastname: Zhan
authors.forename: Wei
authors.initials: W
authors.lastname: Hu
authors.forename: Hongyu
authors.initials: H
authors.lastname: Xiang
authors.forename: Qiuhong
authors.initials: Q
authors.lastname: Xie
mesh_terms: D001234:Aspergillus niger / Q000201:enzymology*; D002942:Circular Dichroism; D004795:Enzyme Stability; D005087:Glucan 1,4-alpha-Glucosidase / Q000737:chemistry* / Q000378:metabolism*; D006031:Glycosylation; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D008970:Molecular Weight; D013012:Sorbitol / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D014199:Trehalose / Q000378:metabolism
chemical_list: D013012:Sorbitol; D014199:Trehalose; D005087:Glucan 1,4-alpha-Glucosidase