title: Novel pathway for alcoholic fermentation of delta-gluconolactone in the yeast Saccharomyces bulderi.
abstract: Under anaerobic conditions, the yeast Saccharomyces bulderi rapidly ferments delta-gluconolactone to ethanol and carbon dioxide. We propose that a novel pathway for delta-gluconolactone fermentation operates in this yeast. In this pathway, delta-gluconolactone is first reduced to glucose via an NADPH-dependent glucose dehydrogenase (EC 1.1.1.47). After phosphorylation, half of the glucose is metabolized via the pentose phosphate pathway, yielding the NADPH required for the glucose-dehydrogenase reaction. The remaining half of the glucose is dissimilated via glycolysis. Involvement of this novel pathway in delta-gluconolactone fermentation in S. bulderi is supported by several experimental observations. (i) Fermentation of delta-gluconolactone and gluconate occurred only at low pH values, at which a substantial fraction of the substrate is present as delta-gluconolactone. Unlike gluconate, the latter compound is a substrate for glucose dehydrogenase. (ii) High activities of an NADP(+)-dependent glucose dehydrogenase were detected in cell extracts of anaerobic, delta-gluconolactone-grown cultures, but activity of this enzyme was not detected in glucose-grown cells. Gluconate kinase activity in cell extracts was negligible. (iii) During anaerobic growth on delta-gluconolactone, CO(2) production exceeded ethanol production by 35%, indicating that pyruvate decarboxylation was not the sole source of CO(2). (iv) Levels of the pentose phosphate pathway enzymes were 10-fold higher in delta-gluconolactone-grown anaerobic cultures than in glucose-grown cultures, consistent with the proposed involvement of this pathway as a primary dissimilatory route in delta-gluconolactone metabolism.
authors.affiliation: Kluyver Laboratory of Biotechnology, Delft University of Technology, Julianalaan 67, 2628 BC Delft, The Netherlands.
authors.forename: Johannes P
authors.initials: JP
authors.lastname: van Dijken
authors.forename: Arjen
authors.initials: A
authors.lastname: van Tuijl
authors.forename: Marijke A H
authors.initials: MA
authors.lastname: Luttik
authors.forename: Wouter J
authors.initials: WJ
authors.lastname: Middelhoven
authors.forename: Jack T
authors.initials: JT
authors.lastname: Pronk
mesh_terms: D000693:Anaerobiosis; D018533:Biomass; D004734:Energy Metabolism; D000431:Ethanol / Q000378:metabolism*; D005285:Fermentation / Q000502:physiology*; D005942:Gluconates / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D042843:Glucose 1-Dehydrogenase; D005948:Glucose Dehydrogenases / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007783:Lactones; D008954:Models, Biological; D008956:Models, Chemical; D009249:NADP / Q000378:metabolism; D012440:Saccharomyces / Q000378:metabolism*
chemical_list: D005942:Gluconates; D007783:Lactones; D000431:Ethanol; D009249:NADP; D005948:Glucose Dehydrogenases; D042843:Glucose 1-Dehydrogenase; D005947:Glucose; C030691:gluconic acid; C010730:beta-glucono-1,5-lactone