Mannose metabolizing enzymes from the red alga Galdieria sulphuraria

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• 作者：Heilmann ; Ingo ; Schnarrenberger ; Claus ; Gross ; Wolfgang
• 关键词：Galdieria sulphuraria ; Rhodophyta ; metabolism ; mannose ; toxicity ; enzymes ; purification ; properties
• 刊名：Phytochemistry
• 出版年：1997
• 出版时间：July, 1997
• 年：1997
• 卷：45
• 期：5
• 页码：903-906
• 全文大小：301 K

文摘

The unicellular thermo-acidophilic rhodophyte Galdieria sulphuraria is capable of growing at high rates on d-mannose, a sugar toxic to many higher plants. Mannose is introduced into metabolism through an ATP-dependent fructokinase which phosphorylates fructose (K_m = 0.21 mM) as well as mannose (K_m = 0.48 mM) but not glucose. The product, mannose-6-phosphate, is converted to fructose-6-phosphate by a mannose-6-phosphate isomerase (K_m = 1.2 mM). The fructokinase was purified by chromatography on DEAE-Fractogel and hydroxylapatite. The enzyme is a homodimer with an M_r of 75 000. The mannose-6-phosphate isomerase was purified by PEG precipitation and affinity chromatography on Affinity-Gel Blue A. The enzyme is a monomer with an M_r of 48 000. The pathway of mannose utilization in G. sulphuraria strongly resembles the reactions of mannose non-sensitive higher plants, while plants with mannose sensitivity lack activity of mannose-6-phosphate isomerase.