Purification and characterization of acid urease from Lactobacillus fermentum

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Abstract
Acid urease was purified to an electrophoretically homogeneous state, and the molecular weight was estimated to be 220 000. The enzyme consisted of three kinds of subunits, designated α, β and λ, with molecular weights of 67 000, 16 800 and 8600, respectively, in a (α1 \2λ1)2 structure. The isoelectric point of the enzyme was 4.8. The nickel content was found to be 1.9 atoms of nickel per α1β2λ1 unit. The amino acid profile was different from those of known bacterial neutral ureases. The enzyme was most active at pH 2 and around 65° C. It was stable between pH 3 and 9, and below 50° C. The K m for urea was 2.7 mM at pH 2. The enzyme activity was inhibited by Ag+, Hg2+, Cu2+, p-chloromercuribenzoate and acetohydroxamate. The enzyme was separated into three subunits by reverse phase HPLC. The amino terminal amino acid sequences of the subunits α, β and λ were Ser-Phe-Asp-Met-, Met-Val-Pro-Gly- and Met-Arg-Leu-Thr-, respectively.