Catalytic properties of d-xylose isomerase from Streptomyces violaceoruber |
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| Affiliation: | 1. Laboratory of Biochemistry, State University of Ghent, B-9000 Ghent, Belgium;2. Plant Genetic Systems, B-9000 Ghent, Belgium;1. Department of Chemistry and Biochemistry, One University Boulevard, University of Missouri–St. Louis, Saint Louis, MO 63121 USA;2. Center for Nanoscience, One University Boulevard, University of Missouri–St. Louis, Saint Louis, MO 63121, USA;1. Faculty of Health Sciences, University of Primorska, Izola, Slovenia;2. Department of Experimental Oncology, Institute of Oncology Ljubljana, Ljubljana, Slovenia;3. Frank Reidy Research Center for Bioelectrics, Old Dominion University, Norfolk, Virginia, USA;4. School of Medical Diagnostic & Translational Sciences, College of Health Sciences, Old Dominion University, Norfolk, Virginia, USA;1. Department of Food Science and Human Nutrition, University of Illinois at Urbana-Champaign, Urbana, IL, USA;2. Carl R. Woese Institute for Genomic Biology, University of Illinois at Urbana-Champaign, Urbana, IL, USA |
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| Abstract: | The catalytic properties and stability of d-xylose isomerase from Streptomyces violaceoruber have been studied. The enzyme was activated by Mg2+, Co2+ and Mn2+ but Ni2+, Ca2+, Zn2+, Cu2+ and Hg were ineffective. Optimum catalytic conditions were obtained at 80°C in the pH range 7.5–9.5 and in the presence of 10 mm Mg2+. The specific activity of the enzyme increased after treatment with 10 mm EDTA (factor 2.4). A further increase of activity (factor 2.0–2.8) was observed after preincubation of the enzyme with Mg2+ or Co2+, the preincubation time depending on the incubation temperature. The thermal stability of the enzyme is very high. At 60°C the enzyme retained optimum activity following 30 days of storage in the presence of 1 mm Co2+ or 10 mm Mg2+. At 80°C, Co2+ is superior as a protector against thermal denaturation. At saturating concentrations of Mg2+ (35°C) the Km-values of the EDTA-treated enzyme with respect to d-xylose and d-glucose were 2.8 and 149 mm and the dissociation constants of the enzyme-Mg2+ complex for xylitol and d-sorbitol were 0.455 and 4.47 mm, respectively. |
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