title: Identification of a salvage pathway for D-arabinose in Mycobacterium smegmatis.
abstract: Extracts of Mycobacterium smegmatis, which was adapted to growth in synthetic medium containing D-arabinose as sole carbon source, catalyzed the NADPH-mediated reduction of D-arabinose to D-arabitol. When arabinose-adapted bacteria were transferred to glycerol medium, resumption of growth was accompanied by a sharp drop in the specific activity of this enzyme. Moreover, extracts of cells grown in D-arabinose medium contained large amounts of an NAD+-linked pentitol dehydrogenase, as compared to bacteria multiplying in glycerol medium. The specific activity of mycobacterial extracts was ten-fold higher for D-arabitol than for its L-isomer, and eight-fold higher than for xylitol (it was more than forty-fold lower in the case of glycerol-grown cells). The product of the pentitol dehydrogenase reaction was identified as D-xylulose by three different procedures. On the basis of these data, it is suggested that utilization of exogenous D-arabinose in mycobacteria involves two dehydrogenases that catalyze the reactions D-arabinose NADPH----D-arabitol NAD+----D-xylulose, by virtue of which an aldopentose is converted into a ketopentose. The alditol: NADP oxidoreductase was isolated from homogenates of D-arabinose-adapted mycobacteria, and purified by DEAE-cellulose chromatography. The enzymatic activity was restricted to a single band which, under denaturing conditions, comigrated with albumin (approximately 46 kDa). It was insensitive to 2-mercaptoethanol, EDTA and NaF, and was inactivated at 70 degrees C.
mesh_terms: D000449:Aldehyde Reductase / Q000378:metabolism; D001089:Arabinose / Q000378:metabolism*; D002845:Chromatography; D004586:Electrophoresis; D008670:Metals / Q000494:pharmacology; D009161:Mycobacterium / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D013401:Sugar Alcohol Dehydrogenases / Q000378:metabolism; D013402:Sugar Alcohols / Q000096:biosynthesis; D013696:Temperature
chemical_list: D008670:Metals; D013402:Sugar Alcohols; D009249:NADP; D001089:Arabinose; D013401:Sugar Alcohol Dehydrogenases; C022751:D-arabinitol dehydrogenase; D000449:Aldehyde Reductase; C014999:arabitol