Evidence for a non-phosphorylated route of galactose breakdown in cell-free extracts of Aspergillus niger

Elshafei, Ali M.; Abdel‐Fatah, Osama M.

doi:10.1016/s0141-0229(01)00346-5

Cited by 36 publications

(34 citation statements)

References 27 publications

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“…A condensation reaction between D-glyceraldehyde and pyruvate using glucose-grown mycelia resulted in the synthesis of D-KDG in a large diastereometric excess (41), indicating that the KDG aldolase in this organism does exhibit facial selectivity. An equivalent, inducible pathway exists in the organism for the catabolism of galactose, involving a separate KDGal aldolase with the opposite facial selectivity (42). The KDGal aldolase has also been investigated in Aspergillus terreus and shown to produce diastereometrically pure D-KDGal in a condensation between D-glyceraldehyde and pyruvate (43).…”

Section: Discussionmentioning

confidence: 99%

Metabolic Pathway Promiscuity in the Archaeon Sulfolobus solfataricus Revealed by Studies on Glucose Dehydrogenase and 2-Keto-3-deoxygluconate Aldolase

Lamble

Heyer

Bull

et al. 2003

Journal of Biological Chemistry

136

206

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The hyperthermophilic Archaeon Sulfolobus solfataricus metabolizes glucose by a non-phosphorylative variant of the Entner-Doudoroff pathway. In this pathway glucose dehydrogenase and gluconate dehydratase catalyze the oxidation of glucose to gluconate and the subsequent dehydration of gluconate to 2-keto-3-deoxygluconate. 2-Keto-3-deoxygluconate (KDG) aldolase then catalyzes the cleavage of 2-keto-3-deoxygluconate to glyceraldehyde and pyruvate. The gene encoding glucose dehydrogenase has been cloned and expressed in Escherichia coli to give a fully active enzyme, with properties indistinguishable from the enzyme purified from S. solfataricus cells. Kinetic analysis revealed the enzyme to have a high catalytic efficiency for both glucose and galactose. KDG aldolase from S. solfataricus has previously been cloned and expressed in E. coli. In the current work its stereoselectivity was investigated by aldol condensation reactions between D-glyceraldehyde and pyruvate; this revealed the enzyme to have an unexpected lack of facial selectivity, yielding approximately equal quantities of 2-keto-3-deoxygluconate and 2-keto-3-deoxygalactonate. The KDG aldolase-catalyzed cleavage reaction was also investigated, and a comparable catalytic efficiency was observed with both compounds. Our evidence suggests that the same enzymes are responsible for the catabolism of both glucose and galactose in this Archaeon. The physiological and evolutionary implications of this observation are discussed in terms of catalytic and metabolic promiscuity.The hyperthermophilic Archaeon Sulfolobus solfataricus grows optimally at 80 -85°C and pH 2-4, utilizing a wide range of carbon and energy sources (1). It has become one of the most comprehensively researched model organisms of archaeal metabolism and bioenergetics (2). Central metabolism in this organism involves a modified Entner-Doudoroff pathway (3), production of acetyl-CoA by pyruvate:ferredoxin oxidoreductase (4), and the citric acid cycle coupled to oxidative phosphorylation (5). The modified Entner-Doudoroff pathway is a nonphosphorylative variant of the classic pathway and proceeds with no net production of ATP (Fig. 1). An analogous pathway has also been detected in the thermoacidophilic Archaea Sulfolobus acidocaldarius (6), Thermoplasma acidophilum (7), and Thermoproteus tenax (8), as well as strains of Aspergillus fungi (9, 10).The first reaction of the non-phosphorylative Entner-Doudoroff pathway involves the NAD(P)-dependent oxidation of glucose to gluconate, catalyzed by glucose dehydrogenase. Gluconate is then dehydrated by gluconate dehydratase to 2-keto-3-deoxygluconate (KDG), 1 which undergoes an aldolate cleavage to pyruvate and glyceraldehyde, catalyzed by KDG aldolase. Glyceraldehyde dehydrogenase then oxidizes glyceraldehyde to glycerate, which is phosphorylated by glycerate kinase to give 2-phosphoglycerate. A second molecule of pyruvate is produced from this by the actions of enolase and pyruvate kinase.Glucose dehydrogenase has previously been purified to homogenei...

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Section: Discussionmentioning

confidence: 99%

Metabolic Pathway Promiscuity in the Archaeon Sulfolobus solfataricus Revealed by Studies on Glucose Dehydrogenase and 2-Keto-3-deoxygluconate Aldolase

Lamble

Heyer

Bull

et al. 2003

Journal of Biological Chemistry

136

206

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“…Here D-galactose is first oxidised, followed by a dehydration, a phosphorylation and an aldolase reaction resulting in pyruvate and D-glyceraldehyde-3-phosphate [2]. A non-phosphorylating variant of this pathway has been described in the eukaryotic microorganism Aspergillus niger [3]. Yet another eukaryotic pathway for D-galactose catabolism was suggested to be active in filamentous fungi.…”

Section: Introductionmentioning

confidence: 99%

Sorbitol dehydrogenase of Aspergillus niger, SdhA, is part of the oxido‐reductive d‐galactose pathway and essential for d‐sorbitol catabolism

et al. 2012

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a b s t r a c tIn filamentous fungi D-galactose can be catabolised through the oxido-reductive and/or the Leloir pathway. In the oxido-reductive pathway D-galactose is converted to D-fructose in a series of steps where the last step is the oxidation of D-sorbitol by an NAD-dependent dehydrogenase. We identified a sorbitol dehydrogenase gene, sdhA (JGI53356), in Aspergillus niger encoding a medium chain dehydrogenase which is involved in D-galactose and D-sorbitol catabolism. The gene is upregulated in the presence of D-galactose, galactitol and D-sorbitol. An sdhA deletion strain showed reduced growth on galactitol and growth on D-sorbitol was completely abolished. The purified enzyme converted D-sorbitol to D-fructose with K m of 50 ± 5 mM and v max of 80 ± 10 U/mg.

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“…D-threo-3-Deoxyhexulosonate is then phosphorylated to D-threo-3-deoxy hexulosonate 6-phosphate, which is subsequently split by an aldolase, resulting in pyruvate and D-glyceraldehyde-3-phosphate. In a strain of the mold Aspergillus niger, a nonphosphorylated alternative of the De Ley-Doudoroff pathway was described where the D-threo-3-deoxy-hexulosonate is split by an aldolase to pyruvate and D-glyceraldehyde instead of being phosphorylated (4).…”

mentioning

confidence: 99%

“…In T. reesei, xylitol dehydrogenase, xdh1, was proposed to be the enzyme responsible for this reaction. 4 Fekete et al (13) suggested that L-sorbose is produced in Aspergillus nidulans from galactitol by L-arabitol dehydrogenase and that it could be further converted to D-sorbitol. The reaction mechanism of the galactitol to L-sorbose conversion, however, has not been proposed and currently remains elusive.…”

mentioning

confidence: 99%

l-xylo-3-Hexulose Reductase Is the Missing Link in the Oxidoreductive Pathway for d-Galactose Catabolism in Filamentous Fungi

Mojžita

Herold

Metz

et al. 2012

Journal of Biological Chemistry

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Background:There is an oxidoreductive D-galactose pathway in filamentous fungi. Results:We identified an L-xylo-3-hexulose reductase that produces D-sorbitol and that is part of this pathway. Conclusion: This L-xylo-3-hexulose reductase is the missing link in the oxidoreductive D-galactose pathway. Significance: The alternative pathway for D-galactose catabolism in filamentous fungi is elucidated.

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Evidence for a non-phosphorylated route of galactose breakdown in cell-free extracts of Aspergillus niger

Cited by 36 publications

References 27 publications

Metabolic Pathway Promiscuity in the Archaeon Sulfolobus solfataricus Revealed by Studies on Glucose Dehydrogenase and 2-Keto-3-deoxygluconate Aldolase

Metabolic Pathway Promiscuity in the Archaeon Sulfolobus solfataricus Revealed by Studies on Glucose Dehydrogenase and 2-Keto-3-deoxygluconate Aldolase

Sorbitol dehydrogenase of Aspergillus niger, SdhA, is part of the oxido‐reductive d‐galactose pathway and essential for d‐sorbitol catabolism

l-xylo-3-Hexulose Reductase Is the Missing Link in the Oxidoreductive Pathway for d-Galactose Catabolism in Filamentous Fungi

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