科研之友
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摘要
Bacillus sp. GRE1 isolated from an Ethiopian hyperthermal spring produced raw-starch digesting, Ca(2+)-independent thermostable alpha-amylase. Enzyme production in shake flask experiments using optimum nutrient supplements and environmental conditions was 2,360 U l(-1). Gel filtration chromatography yielded a purification factor of 33.6-fold and a recovery of 46.5%. The apparent molecular weight of the enzyme was 55 kDa as determined by SDS-PAGE. Presence or absence of Ca(2+) produced similar temperature optima of 65-70 degrees C. The optimum pH was in the range of 5.5-6.0. The enzyme maintained 50% of its original activity after 45 min of incubation at 80 degrees C and was stable at a pH range of 5.0-9.0. The V (max) and K (m) values for soluble starch were 42 mg reducing sugar min(-1) and 4.98 mg starch ml(-1), respectively. Strong inhibitors of enzyme activity included Cu(2+), Zn(2+) and Fe(2+). The enzyme coding gene and the deduced protein translation revealed a characteristic but markedly atypical homology to Bacillus species alpha-amylase sequences. The enzyme hydrolyzed wheat, corn and tapioca starch granules efficiently below their gelatinization temperatures. Rather than the higher oligosaccharides normally produced by Bacillus alpha-amylases operating at high temperatures, maltose was the major hydrolysis product with the present enzyme.
- 出版日期2008-11
