D-xylose catabolism in Bacteroides xylanolyticus X5-1.
The xylose metabolism of Bacteroides xylanolyticus X5-1 was studied by determining specific enzyme activities in cell free extracts, by following 13C-label distribution patterns in growing cultures and by mass balance calculations. Enzyme activities of the pentose phosphate pathway and the Embden-Meyerhof-Parnas pathway were sufficiently high to account for in vivo xylose fermentation to pyruvate via a combination of these two pathways. Pyruvate was mainly oxidized to acetyl-CoA, CO2 and a reduced cofactor (ferredoxin). Part of the pyruvate was converted to acetyl-CoA and formate by means of a pyruvate-formate lyase. Acetyl-CoA was either converted to acetate by a combined action of phosphotransacetylase and acetate kinase or reduced to ethanol by an acetaldehyde dehydrogenase and an ethanol dehydrogenase. The latter two enzymes displayed both a NADH- and a NADPH-linked activity. Cofactor regeneration proceeded via a reduction of intermediates of the metabolism (i.e. acetyl-CoA and acetaldehyde) and via proton reduction. According to the deduced pathway about 2.5 mol ATP are generated per mol of xylose degraded.
Biesterveld
S
S
Department of Microbiology, Agricultural University Wageningen, The Netherlands.
Kok
M D
MD
Dijkema
C
C
Zehnder
A J
AJ
Stams
A J
AJ
D001439:Bacteroides / Q000201:enzymology* / Q000254:growth & development; D001692:Biological Transport; D004734:Energy Metabolism / Q000502:physiology; D005285:Fermentation; D010427:Pentose Phosphate Pathway / Q000502:physiology; D011773:Pyruvates / Q000378:metabolism; D019289:Pyruvic Acid; D014994:Xylose / Q000037:antagonists & inhibitors / Q000378:metabolism*
D011773:Pyruvates; D019289:Pyruvic Acid; D014994:Xylose