Molecular and biochemical characterization of a serine racemase from Arabidopsis thaliana.
A cDNA encoding a homolog of mammalian serine racemase, a unique enzyme in eukaryotes, was isolated from Arabidopsis thaliana and expressed in Escherichia coli cells. The gene product, of which the amino acid residues for binding pyridoxal 5'-phosphate (PLP) are conserved in this as well as mammalian serine racemases, catalyzes not only serine racemization but also dehydration of serine to pyruvate. The enzyme is a homodimer and requires PLP and divalent cations, Ca2+, Mg2+, Mn2+, Fe2+, or Ni2+, at alkaline pH for both activities. The racemization process is highly specific toward L-serine, whereas L-alanine, L-arginine, and L-glutamine were poor substrates. The Vmax/Km values for racemase activity of L- and D-serine are 2.0 and 1.4 nmol/mg/min/mM, respectively, and those values for L- and D-serine on dehydratase activity are 13 and 5.3 nmol/mg/min/mM, i.e. consistent with the theory of racemization reaction and the specificity of dehydration toward L-serine. Hybridization analysis showed that the serine racemase gene was expressed in various organs of A. thaliana.
Fujitani
Yoshiyuki
Y
Research Institute for Bioresources, Okayama University, 2-20-1 Chuo, Kurashiki, Okayama 710-0046, Japan.
Nakajima
Nobuyoshi
N
Ishihara
Koji
K
Oikawa
Tadao
T
Ito
Kazutoshi
K
Sugimoto
Manabu
M
D000409:Alanine / Q000737:chemistry / Q000378:metabolism; D017360:Arabidopsis / Q000201:enzymology*; D001120:Arginine / Q000737:chemistry / Q000378:metabolism; D002384:Catalysis; D002413:Cations, Divalent / Q000494:pharmacology; D019281:Dimerization; D004926:Escherichia coli / Q000166:cytology / Q000235:genetics; D005973:Glutamine / Q000737:chemistry / Q000378:metabolism; D006836:Hydro-Lyases / Q000187:drug effects / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D017404:In Situ Hybridization, Fluorescence; D008670:Metals / Q000494:pharmacology; D008969:Molecular Sequence Data; D011732:Pyridoxal Phosphate / Q000378:metabolism; D019998:Racemases and Epimerases / Q000235:genetics* / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000737:chemistry / Q000378:metabolism; D013237:Stereoisomerism; D013379:Substrate Specificity; D000099300:Serine Racemase
D000409:Alanine; D001120:Arginine; D002413:Cations, Divalent; D005973:Glutamine; D006836:Hydro-Lyases; D008670:Metals; D011732:Pyridoxal Phosphate; D019998:Racemases and Epimerases; D012694:Serine; D000099300:Serine Racemase