title: Pentitol metabolism of Rhodobacter sphaeroides Si4: purification and characterization of a ribitol dehydrogenase.
abstract: The phototrophic bacterium Rhodobacter sphaeroides strain Si4 induced ribitol dehydrogenase (EC 1.1.1.56) when grown on ribitol- or xylitol-containing medium. This ribitol dehydrogenase was purified to apparent homogeneity by ammonium sulphate precipitation, affinity chromatography on Procion red, and chromatography on Q-Sepharose. For the native enzyme an isoelectric point of pH 6.1 and an apparent M(r) of 50,000 was determined. SDS-PAGE yielded a single peptide band of M(r) 25,000 suggesting a dimeric enzyme structure. The ribitol dehydrogenase was specific for NAD+ but unspecific as to its polyol substrate. In order of decreasing activity ribitol, xylitol, erythritol, D-glucitol and D-arabitol were oxidized. The pH optimum of substrate oxidation was 10, and that of substrate reduction was 6.5. The equilibrium constant of the interconversion of ribitol to D-ribulose was determined to be 0.33 nM at pH 7.0 and 25 degrees C. The Km-values determined for ribitol, ribulose, xylitol and NAD+ (in the presence of ribitol) were 6.3, 12.5, 77 and 0.077 mM, respectively. Because of the favourable Km for ribitol, a method for quantitative ribitol determination was elaborated.
authors.affiliation: Institut für Mikrobiologie, Universität Göttingen, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Kahle
authors.forename: K H
authors.initials: KH
authors.lastname: Schneider
authors.forename: F
authors.initials: F
authors.lastname: Giffhorn
mesh_terms: D004790:Enzyme Induction; D004896:Erythritol / Q000378:metabolism; D012242:Rhodobacter sphaeroides / Q000201:enzymology*; D012255:Ribitol / Q000378:metabolism*; D013379:Substrate Specificity; D013401:Sugar Alcohol Dehydrogenases / Q000302:isolation & purification* / Q000378:metabolism; D013402:Sugar Alcohols / Q000378:metabolism; D014993:Xylitol / Q000378:metabolism
chemical_list: D013402:Sugar Alcohols; D012255:Ribitol; D013401:Sugar Alcohol Dehydrogenases; C022529:ribitol 2-dehydrogenase; D004896:Erythritol; D014993:Xylitol