title: Pyruvate catabolism during transient state conditions in chemostat cultures of Enterococcus faecalis NCTC 775: importance of internal pyruvate concentrations and NADH/NAD+ ratios.
abstract: NADH/NAD+ ratios and internal pyruvate concentrations were determined during switches between aerobic and anaerobic steady-state conditions of glucose-limited chemostat cultures of Enterococcus faecalis. During the switch experiments, changes in catabolic fluxes were observed: transition from anaerobic to aerobic conditions resulted in a complete and instantaneous conversion of glucose into acetate and CO2 via the pyruvate dehydrogenase complex, while during a switch from aerobic to anaerobic conditions the culture became homolactic. A similar switch to a homolactic fermentation was observed upon release of the limitation by addition of a glucose pulse to the culture. In sharp contrast to this, a pyruvate pulse resulted in an increase of both pyruvate formate-lyase and pyruvate dehydrogenase complex activity. Furthermore, acetoin was formed during a pyruvate pulse, probably due to a dramatic increase in internal pyruvate concentration. Regulation of the catabolic fluxes over the various pyruvate-catabolizing enzymes is discussed in view of the observed changes in internal pyruvate concentrations and NADH/NAD+ ratios.
authors: Department of Microbiology, University of Amsterdam, The Netherlands.
authors: J L
authors: JL
authors: Snoep
authors: M R
authors: MR
authors: de Graef
authors: M J
authors: MJ
authors: Teixeira de Mattos
authors: O M
authors: OM
authors: Neijssel
mesh_terms: D000085:Acetates / Q000378:metabolism; D000093:Acetoin / Q000378:metabolism; D000123:Acetyltransferases / Q000378:metabolism; D000332:Aerobiosis / Q000502:physiology; D002245:Carbon Dioxide / Q000378:metabolism; D013293:Enterococcus faecalis / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D009243:NAD / Q000378:metabolism*; D010084:Oxidation-Reduction; D011768:Pyruvate Dehydrogenase Complex / Q000378:metabolism; D011773:Pyruvates / Q000378:metabolism*
chemical_list: D000085:Acetates; D011768:Pyruvate Dehydrogenase Complex; D011773:Pyruvates; D009243:NAD; D002245:Carbon Dioxide; D000093:Acetoin; D000123:Acetyltransferases; C022560:formate C-acetyltransferase; D005947:Glucose