title: Purification and characterization of hyperthermotolerant leucine aminopeptidase from Geobacillus thermoleovorans 47b.
abstract: A thermophilic bacterium, which we designated as Geobacillus thermoleovorans 47b was isolated from a hot spring in Beppu, Oita Prefecture, Japan, on the basis of its ability to grow on bitter peptides as a sole carbon and nitrogen source. The cell-free extract from G. thermoleovorans 47b contained leucine aminopeptidase (LAP; EC 3.4.11.10), which was purified 164-fold to homogeneity in seven steps, using ammonium sulfate fractionation followed by the column chromatography using DEAE-Toyopearl, hydroxyapatite, MonoQ and Superdex 200 PC gel filtration, followed again by MonoQ and hydroxyapatite. The enzyme was a single polypeptide with a molecular mass of 42,977.2 Da, as determined by matrix-assisted laser desorption ionization and time-of-flight mass spectrometry, and was found to be thermostable at 90 degrees C for up to 1 h. Its optimal pH and temperature were observed to be 7.6-7.8 and 60 degrees C, respectively, and it had high activity towards the substrates Leu-p-nitroanilide (p-NA)(100%), Arg-p-NA (56.3%) and LeuGlyGly (486%). The K(m) and V(max) values for Leu-p-NA and LeuGlyGly were 0.658 mM and 25.0 mM and 236.2 micromol min(-1) mg(-1) protein and 1,149 micromol min(-1) mg(-1) protein, respectively. The turnover rate (k(cat)) and catalytic efficiency (k(cat)/ K(m)) for Leu-p-NA and LeuGlyGly were 10,179 s(-1) and 49,543 s(-1) and 15,470 mM(-1 ) s(-1) and 1981.7 mM(-1 ) s(-1), respectively. The enzyme was strongly inhibited by EDTA, 1,10-phenanthroline, dithiothreitol, beta-mercaptoethanol, iodoacetate and bestatin; and its apoenzyme was found to be reactivated by Co(2+) .
authors.affiliation: Department of Biology, Faculty of Science, Chiang Mai University, Thailand.
authors.forename: Somkid
authors.initials: S
authors.lastname: Deejing
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Yoshimune
authors.forename: Saisamorn
authors.initials: S
authors.lastname: Lumyong
authors.forename: Mitsuaki
authors.initials: M
authors.lastname: Moriguchi
mesh_terms: D001406:Bacillaceae / Q000201:enzymology*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D004795:Enzyme Stability; D006358:Hot Temperature; D006868:Hydrolysis; D007931:Leucyl Aminopeptidase / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D007931:Leucyl Aminopeptidase