Characterization of a xylitol dehydrogenase and a d-arabitol dehydrogenase from the thermo- and acidophilic red alga Galdieria sulphuraria |
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Authors: | Robert Stein Wolfgang Gross Claus Schnarrenberger |
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Institution: | Institut für Pflanzenphysiologie und Mikrobiologie, Freie Universit?t Berlin, K?nigin-Luise-Strasse 12–16a, D-14195 Berlin, Germany, DE
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Abstract: | Galdieria sulphuraria (Galdieri) Merola can grow heterotrophically on at least ten different polyols. We investigated their metabolic path to glycolysis/gluconeogenesis
and identified two NAD-dependent polyol dehydrogenases. Activity of other enzymes metabolizing mannitol or sorbitol could
not be detected. The two dehydrogenases had a broad substrate specificity and were termed xylitol dehydrogenase (EC 1.1.1.14;
substrate specificity: xylitol > d-sorbitol > d-mannitol > l-arabitol) and d-arabitol dehydrogenase (EC 1.1.1.11; substrate specificity: d-arabitol > l-fucitol > d-mannitol > d-threitol) according to the substrate with the lowest K
m value. The xylitol dehydrogenase was stable during purification. In contrast, the d-arabitol dehydrogenase was thermolabile and depended on divalent ions for stability and activity, preferentially Mn2+ and Ni2+. The molecular mass of the xylitol dehydrogenase was estimated to be 295 kDa by size-exclusion chromatography and 220 kDa
by rate-sedimentation centrifugation. The d-arabitol dehydrogenase had a molecular mass of 105 kDa as determined by rate-sedimentation centrifugation. The specific activity
of both enzymes increased about fourfold when cells were transferred from autotrophic to heterotrophic conditions regardless
of whether sugars or polyols were supplied as substrates. The significance of polyol metabolism in Galdieria sulphuraria with regard to the natural habitat of the alga is discussed.
Received: 15 January 1997 / Accepted: 12 February 1997 |
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Keywords: | :d-Arabitol dehydrogenase Galdieria Polyol metabolism Rhodophyta Xylitol dehydrogenase |
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