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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 15, Number 10
BKCSDE 15(10)
October 20, 1994 

Changes in Optimum pH and Thermostability of α-amylase from Bacillus licheniformis by Site-directed Mutagenesis of His 235 and Asp 328
Mi-Sook Kim, Sang-Kyou Lee, Han-Seung Jung, Chul-Hak Yang
The α-amylase gene of Bacillus licheniformis has been cloned and two mutant α-amylase genes of which histidine 235 was changed to glutamine (H235Q) and aspartic acid 328 to glutamic acid (D328E) have been produced by site-directed mutagenesis. The kinetic parameters, optimum pH and thermostability of wild type(WT) and these two mutant amylases expressed in E. coli MC1061 have been compared after purification. The Km values of WT, H235Q and D328E α-amylases were 0.22%, 0.73%, and 0.80% respectively, when using starch as the substrate. The Vmax values of wild type α -amylase and mutant α-amylases were 0.6-0.7%/minute, and did not show any significant differences among them. The optimum pH of D328E α-amylase was shifted to more acidic pH. Also, the thermostability of H235Q α-amylase was increased compared to the wild type α-amylase.
832 - 835
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