title: UDPgalactose 4-epimerase from Saccharomyces cerevisiae. A bifunctional enzyme with aldose 1-epimerase activity.
abstract: UDPgalactose 4-epimerase (epimerase) catalyzes the reversible conversion between UDPgalactose and UDPglucose and is an important enzyme of the galactose metabolic pathway. The Saccharomyces cerevisiae epimerase encoded by the GAL10 gene is about twice the size of either the bacterial or human protein. Sequence analysis indicates that the yeast epimerase has an N-terminal domain (residues 1-377) that shows significant similarity with Escherichia coli and human UDPgalactose 4-epimerase, and a C-terminal domain (residues 378-699), which shows extensive identity to either the bacterial or human aldose 1-epimerase (mutarotase). The S. cerevisiae epimerase was purified to > 95% homogeneity by sequential chromatography on DEAE-Sephacel and Resource-Q columns. Purified epimerase preparations showed mutarotase activity and could convert either alpha-d-glucose or alpha-d-galactose to their beta-anomers. Induction of cells with galactose led to simultaneous enhancement of both epimerase and mutarotase activities. Size exclusion chromatography experiments confirmed that the mutarotase activity is an intrinsic property of the yeast epimerase and not due to a copurifying endogenous mutarotase. When the purified protein was treated with 5'-UMP and l-arabinose, epimerase activity was completely lost but the mutarotase activity remained unaffected. These results demonstrate that the S. cerevisiae UDPgalactose 4-epimerase is a bifunctional enzyme with aldose 1-epimerase activity. The active sites for these two enzymatic activities are located in different regions of the epimerase holoenzyme.
authors.affiliation: Division of Drug Design, Development and Molecular Modeling, Indian Institute of Chemical Biology, Kolkata, India. majumdar_60@yahoo.com
authors.forename: Siddhartha
authors.initials: S
authors.lastname: Majumdar
authors.forename: Jhuma
authors.initials: J
authors.lastname: Ghatak
authors.forename: Sucheta
authors.initials: S
authors.lastname: Mukherji
authors.forename: Hiranmoy
authors.initials: H
authors.lastname: Bhattacharjee
authors.forename: Amar
authors.initials: A
authors.lastname: Bhaduri
mesh_terms: D000595:Amino Acid Sequence; D001089:Arabinose / Q000737:chemistry / Q000494:pharmacology; D002238:Carbohydrate Epimerases / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism; D003001:Cloning, Molecular; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009904:Optical Rotation; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014534:UDPglucose 4-Epimerase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D014542:Uridine Monophosphate / Q000737:chemistry / Q000494:pharmacology
chemical_list: D004791:Enzyme Inhibitors; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; D001089:Arabinose; D014542:Uridine Monophosphate; D002238:Carbohydrate Epimerases; D014534:UDPglucose 4-Epimerase; C019646:aldose 1-epimerase