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UDP‐galactose 4‐epimerase from Escherichia coli : existence of a catalytic monomer
Author(s) -
Nayar Suprabha,
Bhattacharyya Debasish
Publication year - 1997
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(97)00552-8
Subject(s) - monomer , chemistry , molecular mass , escherichia coli , protein subunit , galactose , nad+ kinase , enzyme , dimer , catalysis , biochemistry , protein quaternary structure , size exclusion chromatography , stereochemistry , organic chemistry , polymer , gene
UDP‐galactose 4‐epimerase from Escherichia coli is a homodimer of molecular mass 39 kDa/subunit and requires NAD as a co‐factor. X‐ray crystallographic studies indicate two pyridine nucleotide co‐factor‐binding sites of the dimeric molecule situated in a symmetry‐oriented manner. Size‐exclusion HPLC of an equilibrium intermediate at 3 M urea suggests a monomeric holoenzyme structure that is catalytically active. Ultracentrifugal studies of the native enzyme in a 5–20% sucrose gradient at low protein concentration also indicate existence of a catalytic monomer. The monomer resembles the dimeric protein in stability and most of its physico–chemical properties.