title: Purification and characterization of aspartate racemase from the bivalve mollusk Scapharca broughtonii.
abstract: High concentrations of D-aspartate occur in blood shell Scapharca broughtonii (Mollusca) tissues. We purified aspartate racemase from the foot muscle of the bivalve to electrophoretic homogeneity. The molecular mass shown by sodium dodecyl sulfate polyacrylamide gel was 39 kDa, while that shown by gel filtration ranged from 51 to 63 kDa. Pyridoxal 5'-phosphate-dependency of the enzyme was demonstrated by its absorption spectrum as well as the effects of amino-oxyacetate and other reagents on the activity and spectrum. The enzyme is highly specific to aspartate and does not racemize L-alanine, L-serine and L-glutamate. It showed the highest activity at pH 8 both in the conversion of L- to D- and D- to L-aspartate, and the optimal temperature was 25 degrees C. V(max) and K(m) values for L-aspartate were 7.39 micromolmin(-1)mg(-1) and 60.4 mM and those for D-aspartate were 22.6 micromolmin(-1)mg(-1) and 159 mM, respectively.
authors.affiliation: Department of Environmental Systems Engineering, Nagaoka University of Technology, Nagaoka, Niigata 940-2188, Japan.
authors.forename: Kimihiko
authors.initials: K
authors.lastname: Shibata
authors.forename: Takashi
authors.initials: T
authors.lastname: Watanabe
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Yoshikawa
authors.forename: Katsumasa
authors.initials: K
authors.lastname: Abe
authors.forename: Shouji
authors.initials: S
authors.lastname: Takahashi
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Kera
authors.forename: Ryo-hei
authors.initials: RH
authors.lastname: Yamada
mesh_terms: D000591:Amino Acid Isomerases / Q000737:chemistry / Q000302:isolation & purification* / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008969:Molecular Sequence Data; D008974:Mollusca / Q000201:enzymology*; D017385:Sequence Homology; D013379:Substrate Specificity; D013696:Temperature
chemical_list: D000591:Amino Acid Isomerases; C019749:aspartate racemase