Aminopeptidase B was purified from goat brain with a purification fold of similar to 280 and a yield of 2.7%. The enzyme revealed a single band on both native acrylamide gel and SDS-PAGE thereby confirming apparent homogeneous preparation and its monomeric nature. The enzyme exhibited a molecular mass of 80.2 kDa and 79.7 kDa on Sephadex G-200 and SDS-PAGE respectively. The pH optimum was 7.4 and the enzyme was stable between pH 6.0 and 9.0. L-Arg-beta NA was the most rapidly hydrolyzed substrate followed by Lys-beta NA. The K(m) value with Arg-beta NA was found to be 0.1 mM. Metal chelating and -SH reactive agents strongly inhibited the enzyme activity. 1,10-Phenanthroline exhibited mixed type of inhibition with a K(i) of 5 x 10(-5) M. The enzyme was highly sensitive to urea. Metal ions like Ni(2+), Cd(2+), Fe(2+) and Hg(2+) inhibited the enzyme, whereas Co(2+), Zn(2+), Mn(2+) and Sn(2+) slightly activated the enzyme. (C) 2009 Elsevier Ltd. All rights reserved.