Note: a dashed line (without arrowheads) between two compound names is meant to imply that the two names are just different instantiations of the same compound -- i.e. one may be a specific name and the other a general name, or they may both represent the same compound in different stages of a polymerization-type pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
Locations of Mapped Genes:
Synonyms: Leloir pathway
|Superclasses:||Biosynthesis → Carbohydrates Biosynthesis → Sugars Biosynthesis → Sugar Nucleotides Biosynthesis|
|Degradation/Utilization/Assimilation → Carbohydrates Degradation → Sugars Degradation → Galactose Degradation|
The biological interconversion of galactose and glucose takes place only by way of the Leloir pathway (here named galactose degradation I (Leloir pathway)) and requires the three enzymes galactokinase , galactose-1-phosphate uridylyltransferase and UDP-glucose 4-epimerase.
The only biological importance of these enzymes appears to be to provide for the interconversion of galactosyl and glucosyl groups. galactose-1-epimerase also participates by producing the galactokinase substrate α-D-galactose from its β-anomer [Frey96]. The cycle requires an initial amount of UDP-D-glucose, which is produced by UTP--glucose-1-phosphate uridylyltransferase (EC 126.96.36.199) [Neidhardt96]
Frey96: Frey PA (1996). "The Leloir pathway: a mechanistic imperative for three enzymes to change the stereochemical configuration of a single carbon in galactose." FASEB J 10(4);461-70. PMID: 8647345
Neidhardt96: Neidhardt FC, Curtiss III R, Ingraham JL, Lin ECC, Low Jr KB, Magasanik B, Reznikoff WS, Riley M, Schaechter M, Umbarger HE "Escherichia coli and Salmonella, Cellular and Molecular Biology, Second Edition." American Society for Microbiology, Washington, D.C., 1996.
Arabshahi86: Arabshahi A, Brody RS, Smallwood A, Tsai TC, Frey PA (1986). "Galactose-1-phosphate uridylyltransferase. Purification of the enzyme and stereochemical course of each step of the double-displacement mechanism." Biochemistry 25(19);5583-9. PMID: 3022797
Arabshahi88: Arabshahi A, Flentke GR, Frey PA (1988). "Uridine diphosphate galactose 4-epimerase. pH dependence of the reduction of NAD+ by a substrate analog." J Biol Chem 263(6);2638-43. PMID: 3277958
Bauer91: Bauer AJ, Rayment I, Frey PA, Holden HM (1991). "The isolation, purification, and preliminary crystallographic characterization of UDP-galactose-4-epimerase from Escherichia coli." Proteins 9(2);135-42. PMID: 2008433
Bauer92: Bauer AJ, Rayment I, Frey PA, Holden HM (1992). "The molecular structure of UDP-galactose 4-epimerase from Escherichia coli determined at 2.5 A resolution." Proteins 12(4);372-81. PMID: 1579570
Berger01a: Berger E, Arabshahi A, Wei Y, Schilling JF, Frey PA (2001). "Acid-base catalysis by UDP-galactose 4-epimerase: correlations of kinetically measured acid dissociation constants with thermodynamic values for tyrosine 149." Biochemistry 40(22);6699-705. PMID: 11380265
Bhattacharyya99: Bhattacharyya U, Dhar G, Bhaduri A (1999). "An arginine residue is essential for stretching and binding of the substrate on UDP-glucose-4-epimerase from Escherichia coli. Use of a stacked and quenched uridine nucleotide fluorophore as probe." J Biol Chem 274(21);14573-8. PMID: 10329648
Bingham87: Bingham AH, Busby SJ (1987). "Translation of galE and coordination of galactose operon expression in Escherichia coli: effects of insertions and deletions in the non-translated leader sequence." Mol Microbiol 1(1);117-24. PMID: 2838723
Blackburn76: Blackburn P, Ferdinand W (1976). "The concerted inactivation of Escherichia coli uridine diphosphate galactose 4-epimerase by sugar nucleotide together with a free sugar." Biochem J 155(2);225-9. PMID: 779771
Bork93: Bork P, Sander C, Valencia A (1993). "Convergent evolution of similar enzymatic function on different protein folds: the hexokinase, ribokinase, and galactokinase families of sugar kinases." Protein Sci 2(1);31-40. PMID: 8382990
Burke93: Burke JR, Frey PA (1993). "The importance of binding energy in catalysis of hydride transfer by UDP-galactose 4-epimerase: a 13C and 15N NMR and kinetic study." Biochemistry 1993;32(48);13220-30. PMID: 8241177
Debouck85: Debouck C, Riccio A, Schumperli D, McKenney K, Jeffers J, Hughes C, Rosenberg M, Heusterspreute M, Brunel F, Davison J (1985). "Structure of the galactokinase gene of Escherichia coli, the last (?) gene of the gal operon." Nucleic Acids Res 13(6);1841-53. PMID: 3158881
Deeley75: Deeley R, Blackburn P, Ferdinand W (1975). "The first enzyme of the gal operon in inducible and operator-constitutive strains of Escherichia coli. A comparison of the porperties and amino-terminal sequences of UDP galactose 4-epimerase." Eur J Biochem 60(2);371-7. PMID: 1107041
DiazMejia09: Diaz-Mejia JJ, Babu M, Emili A (2009). "Computational and experimental approaches to chart the Escherichia coli cell-envelope-associated proteome and interactome." FEMS Microbiol Rev 33(1);66-97. PMID: 19054114
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