2.02015-09-08 17:50:01 -06002015-09-14 16:46:09 -0600ECMDB24194M2MDB006311 L-ribulose 5-phosphateL-Ribulose 5-phosphate is a member of the chemical class known as Pentoses. These are monosaccharides in which the carbohydrate moiety contains five carbon atoms. In Escherichia coli, RpiA catalyzes the interconversion of ribose-5-phosphate and ribulose-5-phosphate and is a key enzyme in the pentose phosphate pathway. (PMID 12182339) Interconversion of D-ribose-5-phosphate (R5P) and D-ribulose-5-phosphate is an important step in the pentose phosphate pathway. (PMID 18640127) A key player in LPS synthesis is the enzyme D-arabinose-5-phosphate isomerase (API), which catalyzes the reversible isomerization of D-ribulose-5-phosphate to D-arabinose-5-phosphate, a precursor of 3-deoxy-D-manno-octulosonate that is an essential residue of the LPS inner core. (PMID 20954237) Dihydroxybutanone phosphate synthase (DS) catalyzes a commitment step in riboflavin biosynthesis where ribulose 5-phosphate is converted to dihydroxybutanone phosphate and formate. (PMID 11053863) Ribose-5-phosphate isomerase A (RpiA) plays an important role in interconverting between ribose-5-phosphate (R5P) and ribulose-5-phosphate in the pentose phosphate pathway and the Calvin cycle. (PMID 19214439) L-Ribulose 5-phosphoric acidC5H9O8P228.094228.004601408(3S,4S)-1,3,4-trihydroxy-5-(phosphonatooxy)pentan-2-oneL-ribulose 5-phosphate(2-)OCC(=O)[C@@H](O)[C@@H](O)COP([O-])([O-])=OInChI=1S/C5H11O8P/c6-1-3(7)5(9)4(8)2-13-14(10,11)12/h4-6,8-9H,1-2H2,(H2,10,11,12)/p-2/t4-,5+/m0/s1FNZLKVNUWIIPSJ-CRCLSJGQSA-Llogp-1.86logs-0.63solubility6.23e+01 g/llogp-2.8pka_strongest_acidic1.48pka_strongest_basic-3.3iupac(3S,4S)-1,3,4-trihydroxy-5-(phosphonatooxy)pentan-2-oneaverage_mass228.094mono_mass228.004601408smilesOCC(=O)[C@@H](O)[C@@H](O)COP([O-])([O-])=OformulaC5H9O8PinchiInChI=1S/C5H11O8P/c6-1-3(7)5(9)4(8)2-13-14(10,11)12/h4-6,8-9H,1-2H2,(H2,10,11,12)/p-2/t4-,5+/m0/s1inchikeyFNZLKVNUWIIPSJ-CRCLSJGQSA-Lpolar_surface_area150.18refractivity40.23polarizability17.59rotatable_bond_count6acceptor_count7donor_count3physiological_charge-2formal_charge-2Ascorbate metabolismE. coli is able to utilize L-ascorbate (vitamin C) as the sole source of carbon under anaerobic and aerobic conditions.
Ascorbic acid in the cytoplasm is processed through a spontaneous reaction with a hydrogen ion and hydrogen peroxide, producing water, dehydroascorbic acid and ascorbic acid. Dehydroascorbic acid reacts with water spontaneously producing an isomer, dehydroascorbate (bicyclic form). The compound then loses a hydrogen ion resulting in a 2,3-Diketo-L-gulonate. This compound is then reduced through a NADH dependent 2,3 diketo-L-gulonate reductase, releasing a NAD and 3-Dehydro-L-gulonate.This compound is phosphorylated through an ATP mediated L-xylulose/3-keto-L-gulonate kinase resulting in an ADP, hydrogen ion and a 3-Keto-L-gulonate 6 phosphate.
L-ascorbate can also be imported and converted to L-ascorbate-6-phosphate by the L-ascorbate PTS transporter. L-ascorbate-6-phosphate reacts with a probable L-ascorbate-6-phosphate lactonase ulaG, resulting in a 3-keto-L-gulonate 6-phosphate.
The compound 3-keto-L-gulonate 6-phosphate can be processed aerobically or anaerobically.
Aerobic:
3-keto-L-gulonate 6-phosphate is decarboxylated by a 3-keto-L-gulonate-6-phosphate decarboxylase ulaD, releasing carbon dioxide and L-xylulose-5-phosphate. This compound in turn is changed into an isomer by L-ribulose-5-phosphate 3-epimerase ulaE, resulting in L-ribulose 5-phosphate. This compound again changes into a different isomer through a L-ribulose-5-phosphate 4-epimerase ulaF resulting in Xylulose 5-phosphate. This compound can then be part of the pentose phosphate pathway.
Anaerobic:
3-keto-L-gulonate 6-phosphate is decarboxylated by 3-keto-L-gulonate 6-phosphate decarboxylase sgbH, releasing carbon dioxide and L-xylulose-5-phosphate. This compound in turn is changed into an isomer by predicted L-xylulose 5-phosphate 3-epimerase, resulting in L-ribulose 5-phosphate. This compound again changes into a different isomer through a L-ribulose-5-phosphate 4-epimerase resulting in Xylulose 5-phosphate. This compound can then be part of the pentose phosphate pathway.
Expression of the ula regulon is regulated by the L-ascorbate 6-phosphate-binding repressor UlaR and by cAMP-CRP.
Under aerobic conditions, metabolism of L-ascorbate is hindered by the special reactivity and toxicity of this compound in the presence of oxygen.PW000793MetabolicL-arabinose Degradation IBecause L-arabinose enters E. coli either by a low-affinity proton-driven transporter (AraE) or a high-affinity ATP-driven system (AraFGH), its first intracellular form is unphosphorylated. Then an isomerase and a kinase convert it to L-ribulose-5-phosphate. An epimerase converts L-ribulose-5-phosphate to D-xylulose-5-phosphate, an intermediate of the pentose phosphate pathway, which thereby flows through the pathways of central metabolism to satisfy the cell's need for precursor metabolites, reducing power, and metabolic energy. (EcoCyc)PW002103MetabolicL-lyxose DegradationL-lyxose is an uncommon sugar in nature, and wild-type E. coli can not utilize it as a sole source of carbon and energy. However, mutations can arise that allow E. coli to metabolize L-lyxose through the use of enzymes of the rhamnose, arabinose and 2,3-diketo-L-gulonate systems.
L-lyxose enters the cell through the rhaT-encoded rhamnose transporter. It is then isomerized to L-xylulose by L-rhamnose isomerase.
Two types of mutations then allow further utilization of L-xylulose. Not shown here, a mutated from of L-rhamnulose kinase can phosphorylate L-xylulose, yielding L-xylulose-1-phosphate. Further metabolism to dihydroxyacetone phosphate and glycolate occurs through the rhamnulose-1-phosphate aldolase and aldehyde dehydrogenase A, NAD-linked enzymes. These products can enter glycolate degradation and glycolysis.
As shown here, L-xylulose can be phosphorylated by L-xylulose kinase in a mutant in which YiaJ, the repressor for the yiaKLMNO-lyxK-sgbHUE operon, has been disrupted. L-xylulose-5-phosphate is then further metabolized by predicted L-xylulose 5-phosphate 3-epimerase (so far only a predicted function) and either of two L-ribulose 5-phosphate 4-epimerases (SgbE or AraD) to D-xylulose-5-phosphate, which then enters the pentose phosphate pathway (non-oxidative branch).
The enzymes of L-rhamnose degradation I and L-arabinose degradation I are inducible by L-lyxose as well. (EcoCyc)PW002100MetabolicSpecdb::NmrOneD294015Specdb::NmrOneD294016Specdb::NmrOneD294017Specdb::NmrOneD294018Specdb::NmrOneD294019Specdb::NmrOneD294020Specdb::NmrOneD294021Specdb::NmrOneD294022Specdb::NmrOneD294023Specdb::NmrOneD294024Specdb::NmrOneD294025Specdb::NmrOneD294026Specdb::NmrOneD294027Specdb::NmrOneD294028Specdb::NmrOneD294029Specdb::NmrOneD294030Specdb::NmrOneD294031Specdb::NmrOneD294032Specdb::NmrOneD294033Specdb::NmrOneD294034Specdb::MsMs27281Specdb::MsMs27282Specdb::MsMs27283Specdb::MsMs33839Specdb::MsMs33840Specdb::MsMs33841RibulokinaseP08204ARAB_ECOLIaraBhttp://ecmdb.ca/proteins/P08204.xmlL-ribulose-5-phosphate 4-epimerase sgbEP37680SGBE_ECOLIsgbEhttp://ecmdb.ca/proteins/P37680.xmlL-ribulose-5-phosphate 3-epimerase ulaEP39305ULAE_ECOLIulaEhttp://ecmdb.ca/proteins/P39305.xmlL-ribulose-5-phosphate 4-epimerase ulaFP39306ULAF_ECOLIulaFhttp://ecmdb.ca/proteins/P39306.xmlpredicted L-xylulose 5-phosphate 3-epimeraseP37679yiaRhttp://ecmdb.ca/proteins/P37679.xmlXylulose 5-phosphate + Xylulose 5-phosphate > L-ribulose 5-phosphate + L-ribulose 5-phosphatePW_R002706L-xylulose -5-phosphate + L-Xylulose 5-phosphate > L-ribulose 5-phosphate + L-ribulose 5-phosphatePW_R002710 L-ribulose 5-phosphate + L-ribulose 5-phosphate > Xylulose 5-phosphate + Xylulose 5-phosphatePW_R002707L-Ribulose + Adenosine triphosphate > L-ribulose 5-phosphate + ADP + Hydrogen ionPW_R006133L-Xylulose 5-phosphate > L-ribulose 5-phosphatePW_R006126 L-ribulose 5-phosphate <> Xylulose 5-phosphatePW_R006127