Thermostability of three α-amylases of Streptomyces sp IMD 2679

• Published in: Journal of industrial microbiology & biotechnology Vol. 22; no. 2; pp. 96 - 99
• Main Authors: MCMAHON, H. E. M, KELLY, C. T, FOGARTY, W. M
• Format: Journal Article
• Language: English
• Published: Heidelberg Springer 01.02.1999
• Subjects: Biological and medical sciences; Biology of microorganisms of confirmed or potential industrial interest; Biotechnology; Fundamental and applied biological sciences. Psychology; Miscellaneous; Mission oriented research; Streptomyces; Streptomycetaceae; Enzyme; Streptomyces; Structure function relationship; Thermal stability; Actinomycetales; Glycosidases; Aminoacid; Bacteria; Hydrolases; Actinomycetes; Chemical composition; α-Amylase; O-Glycosidases; Dimerization
• ISSN: 1367-5435; 1476-5535
• DOI: 10.1038/sj.jim.2900612

The amylolytic system of Streptomyces sp IMD 2679 is composed of three alpha -amylases, amylase I, II and III, with temperature maxima of 60, 60-65 and 65 degree C, respectively. Although each alpha -amylase displayed higher stability in the pH range 6.0-8.5 than at pH 5.0-5.5, differences in their thermostabilities were more evident as the pH increased from pH 6.0 to 8.5. There was a 14-min difference in half-lives between amylase III, the most thermostable enzyme and amylase II at pH 6.0, and a 46-min difference in the half-lives of amylase III and the least thermostable enzyme, amylase I at pH 6.5. In addition, the alpha -amylases underwent a pH-dependent monomer-dimer transformation. Increased thermostability of the alpha -amylases was reflected in the variable contents of amino acids (Arg, His, Ser) responsible for electrostatic interactions, and in the levels of aliphatic and bulky hydrophobic amino acids. There was a two-fold reduction in Cys levels in amylase III relative to amylase I and II.