title: Isolation and characterization of urease from Aspergillus niger.
abstract: Urease was purified (4126-fold) from Aspergillus niger (NRRL 003) to a homologous enzyme preparation with a specific activity of 1341 mumol min-1 (mg protein)-1. One species of urease was detected in A. niger, with Km = 3.0 mM, native molecular mass 250,000 Da, pH optimum of 8.0 and a high specificity for urea. Hydroxyurea was a strong competitive inhibitor of urease activity, while N-methylurea acted as a weak uncompetitive inhibitor, based on Lineweaver-Burk and Eadie-Hoftstee plots. The activity of urease was enhanced by, but not dependent on, the presence of Na2EDTA, DL-dithiothreitol (< or = 0.1 to 5.0 mM), Ca2+, Ba2+ and citrate (2 to 20 mM). Urease activity was not affected by Na+, K+, Cl-, Br-, acetate or nitrate (2 to 20 mM), but was significantly decreased in the presence of Li+, Ni2+, Mg2+, Zn2+ or I-. Urease activity decreased 26.0% after 30 min at 65 degrees C, and 86.5% and 100.0% after 5 and 1 min at 80 and 100 degrees C, respectively. Urease activity decreased 30.5% after 90 d at 4 degrees C and 21.0% after 28 d at -20 or -80 degrees C.
authors.affiliation: United States Department of Agriculture, Western Regional Research Center, Process Biotechnology Research Unit, Albany, CA 94710.
authors.forename: P T
authors.initials: PT
authors.lastname: Smith
authors.forename: A D
authors.initials: AD
authors.lastname: King
authors.forename: N
authors.initials: N
authors.lastname: Goodman
mesh_terms: D000838:Anions / Q000494:pharmacology; D001234:Aspergillus niger / Q000201:enzymology*; D002412:Cations / Q000494:pharmacology; D004229:Dithiothreitol / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D004795:Enzyme Stability; D004800:Enzymes, Immobilized / Q000378:metabolism; D006358:Hot Temperature; D008970:Molecular Weight; D014508:Urea / Q000031:analogs & derivatives / Q000378:metabolism*; D014510:Urease / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D000838:Anions; D002412:Cations; D004800:Enzymes, Immobilized; D014508:Urea; D004492:Edetic Acid; D014510:Urease; D004229:Dithiothreitol