TAILIEUCHUNG - Báo cáo khoa học: Molecular identification of monomeric aspartate racemase from Bifidobacterium bifidum

Bifidobacteriumbifidumis a useful probiotic agent exhibiting health-promoting properties and containsD-aspartate as an essential component of the cross-linker moiety in the pepti-doglycan. To help understandD-aspartate biosynthesis in B. bifidumNBRC 14252, aspartate racemase, which cata-lyzes the racemization ofD-andL-aspartate, was purified to homogeneity and characterized. The enzyme was a mono-mer with amolecularmass of 27 kDa. This is the first report showing the presence of a monomeric aspartate racemase | Eur. J. Biochem. 271 4798-4803 2004 FEBS 2004 doi Molecular identification of monomeric aspartate racemase from Bifidobacterium bifidum Tatsuyuki Yamashita1 Makoto Ashiuchi1 Kouhei Ohnishi2 Shin ichiro Kato2 Shinji Nagata1 and Haruo Misono1 2 1 Department of Bioresources Science Kochi University Nankoku Kochi Japan 2Research Institute of Molecular Genetics Kochi University Nankoku Kochi Japan Bifidobacterium bifidum is a useful probiotic agent exhibiting health-promoting properties and contains D-aspartate as an essential component of the cross-linker moiety in the peptidoglycan. To help understand D-aspartate biosynthesis in B. bifidum NBRC 14252 aspartate racemase which catalyzes the racemization of D- and L-aspartate was purified to homogeneity and characterized. The enzyme was a monomer with a molecular mass of 27 kDa. This is the first report showing the presence of a monomeric aspartate racemase. Its enzymologic properties such as its lack of cofactor requirement and susceptibility to thiol-modifying reagents in catalysis were similar to those of the dimeric aspartate racemase from Streptococcus thermophilus. The monomeric enzyme however showed a novel characteristic namely that its thermal stability significantly increased in the presence of aspartate especially the D-enantiomer. The gene encoding the monomeric aspartate racemase was cloned and overexpressed in Escherichia coli cells. The nucleotide sequence of the aspartate racemase gene encoded a peptide containing 241 amino acids with a calculated molecular mass of 26 784 Da. The recombinant enzyme was purified to homogeneity and its properties were almost the same as those of the B. bifidum enzyme. Keywords aspartate racemase Bifidobacterium bifidum D-aspartate peptidoglycan probiotic agent. Bifidobacteria including Bifidobacterium bifidum have been applied widely as probiotic agents exhibiting health-promoting properties. Recent research suggested very interesting .

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