Bacterial Guanidinobutyrase: Variation of substrate specificity by bound divalent metal ions

Abstract

Guanidinobutyrase purified from Arthrobacter sp. does not contain Mn²⁺. but about 1.0 mol of Zn²⁺ per mol of subunit. The enzyme was completely inactivated by 1,10-phenanthroline. The inactivated enzyme was markedly reactivated by incubation with Zn²⁺ or Co²⁺. The replacement of Zn²⁺ by Co²⁺ resulted in significant changes in Vmax values without any change in the Km values for substrates, 4-guanidinobutyrate and D-arginine. The results suggest that the main function of the metal ion is not in binding of substrate to the enzyme, but is in the hydrolysis of the substrate. The reconstituted enzymes with Co²⁺ (Co²⁺-enzyme) showed a different substrate specificity from that of Zn²⁺-enzyme. The predicted amino acid sequence of the enzyme consists of three regions of high homology to Mn²⁺-dependent amidinohydrolases as agmatinase of Escherichia coli, and arginases of Bacillus subtilis and rat liver.