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 tenfold higher for D‐arabitol than for its L‐isomer, and eightfold higher than for xylitol (it was more than fortyfold 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 D‐arabitol 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 (∼ 46 kDa). It was insensitive to 2‐mercaptoethanol, EDTA and NaF, and was inactivated at 70°C. Copyright © 1988, Wiley Blackwell. All rights reserved