Manganese is essential for catalytic activity of Escherichia coli agmatinase

Purified Escherichia coli agmatinase (EC 3.5.3.11) expressed the same activ ity in the absence or presence of added Mn2+ (0-5mM). However, it was stron gly inhibited by Co2+, Ni2+, and Zn2+ and almost half inactivated by EDTA, Partial inactivation by EDTA yielded enzyme species containing 0.85 +/- 0.1 Mn2+/subunit, and it was accompanied by a decrease in intensity of fluores cence emission and a red shift from the emission maximum of 340 nm to 346 n m, indicating the movement of tryptophane residues to a more polar environm ent. The activity and fluorescence properties of fully activated agmatinase were restored by incubation of dialysed species with Mn2+. Manganese-free species, obtained by treatment with EDTA and guanidinium chloride (3 M), we re active only in the presence of added Mn2+. Results obtained, which repre sent the first demonstration of the essentiality of Mn2+ for agmatinase act ivity, are discussed in connection with a possible binuclear metal center i n the enzyme. (C) 1999 Academic Press.