科研之友
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摘要
Screening for cyclodextrin glycosyltransferase (CGTase)-producing alkaliphilic bacteria from samples collected from hyper saline soda lakes (Wadi Natrun Valley, Egypt), resulted in isolation of potent CGTase producing alkaliphilic bacterium, termed NPST-10. 16S rDNA sequence analysis identified the isolate as Amphibacillus sp. CGTase was purified to homogeneity up to 22.1 fold by starch adsorption and anion exchange chromatography with a yield of 44.7%. The purified enzyme was a monomeric protein with an estimated molecular weight of 92 kDa using SDS-PAGE. Catalytic activities of the enzyme were found to be 88.8 U mg(-1) protein, 20.0 U mg(-1) protein and 11.0 U mg(-1) protein for cyclization, coupling and hydrolytic activities, respectively. The enzyme was stable over a wide pH range from pH 5.0 to 11.0, with a maximal activity at pH 8.0. CGTase exhibited activity over a wide temperature range from 45 degrees C to 70 degrees C, with maximal activity at 50 degrees C and was stable at 30 degrees C to 55 degrees C for at least 1 h. Thermal stability of the purified enzyme could be significantly improved in the presence of CaCl2. K-m and V-max values were estimated using soluble starch as a substrate to be 1.7 +/- 0.15 mg/mL and 100 +/- 2.0 mu mol/min, respectively. CGTase was significantly inhibited in the presence of Co2+, Zn2+, Cu2+, Hg2+, Ba2+, Cd2+, and 2-mercaptoethanol. To the best of our knowledge, this is the first report of CGTase production by Amphibacillus sp. The achieved high conversion of insoluble raw corn starch into cyclodextrins (67.2%) with production of mainly beta-CD (86.4%), makes Amphibacillus sp. NPST-10 desirable for the cyclodextrin production industry.
- 出版日期2012-8
