Purification and Properties of Urease from Brevibacterium ammoniagenes

Abstract

Urease was purified to a homogeneousstate from cell-free extracts of a strain of Brevibacterium ammoniagenes.The enzymewas found to have a molecular weight of 200, 000, to consist of three identical subunits with a molecular weight of 67, 000, and to have an isoelectric point at pH 4. 1. The amino acid profile was similar to that of jack bean urease. Methionine and leucine were shown to be the N- and C-terminal residues, respectively. The enzyme contained 1 atom of nickel per subunit. The enzyme was most active at about pH 7 and at 65°C, and was stable betweeen pH 7 and 10 (at 30°C for 5hr) and below 50°C (at pH 7.5 for 1Omin). Among the compounds examined, Hg²⁺, Cu²⁺, PCMB, and hydroxyurea inhibited the enzyme strongly. The Km value of enzyme for urea was found to vary from 18 to 72mMdepending on pH and the type of buffer used. It was proved that the enzymecan be used for the determination of urea by the reaction rate assay method.