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Induction and Characterization of B - Galactosidase in an Extreme Thermophile

出版	American Society for Microbiology, 1972
URL	http://books.google.com.hk/books?id=bWMAzwEACAAJ&hl=&source=gbs_api

註釋A thermostable , B-galactosidase (EC 3.2.1.23; /3-Dgalactoside galactohydrolase) was found to be inducible in an extreme thermophile resembling Thermus aquaticus. Enzyme induction was achieved by the addition of lactose, galactose, or the a-galactoside, melibiose, to growing cultures. The addition of glucose to induced cultures had a repressive effect on further enzyme synthesis. The enzyme was purified 78-fold, and the optimum temperature and pH for activity were determined to be 80 C and pH 5.0, respectively. The enzyme was activated by both manganese and ferrous iron. Sulfhydryl activation and thermal stabilization indicate that the thermophilic , B-galactosidase is a sulfhydryl enzyme. Kinetic determinations at 80 C established a Km of 2.0 x 10-3 M for the chromogenic substrate o-nitrophenyl fl-D-galactopyranoside (ONPG) and a K, of 7.5 x 10-3 M for lactose. The Arrhenius energy of activation (for the hydrolysis of ONPG) was calculated to be 13.7 kcal/mole. A molecular weight of 5.7 x 105 daltons was estimated by elution of the enzyme from Sephadex 4B.