This view shows enzymes only for those organisms listed below, in the list of taxa known to possess the pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Synonyms: diketo-hydrolase pathway
|Superclasses:||Degradation/Utilization/Assimilation → Carbohydrates Degradation → Sugars Degradation → L-rhamnose Degradation|
Some taxa known to possess this pathway include : Sphingomonas sp. SKA58
Expected Taxonomic Range: Bacteria
L-rhamnose is a 6-deoxy-aldohexose that occurs in nature. Some fungi and bacteria posess an L-rhamnose degradation pathway that involves non-phosphorylated intermediates (see pathway L-rhamnose degradation II), analogous to the Entner-Doudoroff pathway II (non-phosphorylative). Pathway L-rhamnose degradation II is in contrast to the known bacterial L-rhamnose degradation pathway which involves phosphorylated intermediates (see L-rhamnose degradation I). Genes encoding enzymes of pathway L-rhamnose degradation II in Scheffersomyces stipitis CBS 6054 (previously known as Pichia stipitis), Debaryomyces hansenii hansenii CBS767 and Azotobacter vinelandii NBRC 102612 have been cloned, expressed and their products functionally characterized. Phylogenetic studies of the fungal and bacterial 2-keto-3-deoxy-L-rhamnoate aldolases (L-KDR aldolases) suggested that they are unerelated evolutionarily. Their respective non-phosphorylative L-rhamnose degradation pathways appear to have evolved independently and are the result of convergent evolution (in [Watanabe08] and in [Watanabe09]). In Sphingomonas sp. SKA58, a variation of this non-phosphorylative pathway was demonstrated in which 2-dehydro-3-deoxy-L-rhamnonate is oxidized to L-2,4-diketo-3-deoxyrhamnonate, followed by hydrolysis of this compound to pyruvate and (S)-lactate (L-lactate) [Watanabe09] (this pathway).
About This Pathway
The first reaction in this pathway shows the spontaneous conversion of the pyranose ring form of L-rhamnose to its furanose ring form L-rhamnofuranose (the α and β anomers of each form are not specified here). This reaction is shown because the reaction that follows is catalyzed by L-rhamnose 1-dehydrogenase (EC 184.108.40.206) which specifies L-rhamnofuranose as a substrate and L-rhamnono-1,4-lactone (L-rhamnono-γ-lactone) as a product. As noted in [Dahms72], a δ-lactone (1,5-lactone) would be produced by a pyranose ring form).
In Sphingomonas sp. SKA58 the first three enzymatic reactions are shared with pathway L-rhamnose degradation II, but the last two reactions of the pathway were shown to be catalyzed by L-2-keto-3-deoxyrhamnoate 4-dehydrogenase and L-2,4-diketo-3-deoxyrhamnoate hydrolase encoded by genes lra5 and lra6, respectively. pyruvate and (S)-lactate (L-lactate) are the end products of this variant and (S)-lactaldehyde is not produced [Watanabe09].
Watanabe08: Watanabe S, Saimura M, Makino K (2008). "Eukaryotic and bacterial gene clusters related to an alternative pathway of nonphosphorylated L-rhamnose metabolism." J Biol Chem 283(29);20372-82. PMID: 18505728
Rakus08: Rakus JF, Fedorov AA, Fedorov EV, Glasner ME, Hubbard BK, Delli JD, Babbitt PC, Almo SC, Gerlt JA (2008). "Evolution of enzymatic activities in the enolase superfamily: L-rhamnonate dehydratase." Biochemistry 47(38);9944-54. PMID: 18754693
Ryu04: Ryu KS, Kim C, Kim I, Yoo S, Choi BS, Park C (2004). "NMR application probes a novel and ubiquitous family of enzymes that alter monosaccharide configuration." J Biol Chem 279(24);25544-8. PMID: 15060078
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