D-arginase of Arthrobacter sp KUJ 8602:: Characterization and its identity with Zn2+-guanidinobutyrase

D-Arginase activity was found in the cells of an isolate, Arthrobacter sp. KUJ 8602, grown in the L-arginine medium, and the enzyme was purified and characterized. Its molecular weight was estimated to be about 232,000 by gel filtration, and that of the subunit was approximately 40,000 by SDS-PAGE, suggesting that the enzyme is a homohexamer. The enzyme acted on not only D-arginine but also 4-guanidinobutyrate, 3-guanidinopropionate and even L-arginine. The V-max/K-m values for 4-guanidinobutyrate and D-arginine were determined to be 87 and 0.81 mumol/min/mg/mM, respectively. Accordingly, the enzyme is regarded as a kind of guanidinobutyrase [EC 3.5.3.7]. The pH optima for 4-guanidinobutyrate and D-arginine were 9.0 and 9.5, respectively. The enzyme was inhibited competitively by 5-aminovalerate, and thiol carboxylates such as mercaptoacetate served as strong mixed-type inhibitors. The enzyme contained about 1 g-atom of firmly bound Zn2+ per mol of subunit, and removal of the metal ions by incubation with 1,10-phenanthroline resulted in loss of activity. The inactivated enzyme was reactivated markedly by incubation with either Zn2+ or Co2+, and slightly by incubation with Mn2+. The nucleotide sequence of enzyme contains an open reading frame that encodes a polypeptide of 353 amino acid residues (M,: 37,933). The predicted amino acid sequence contains sequences involved in the binding of metal ions and the guanidino group of the substrate, which show a high homology with corresponding sequences of Mn2+-dependent amidinohydrolases such as agmatinase from Escherichia coli and L-arginase from rat liver, though the homology of their entire sequences is relatively low (24-43%).