title: Purification and molecular characterization of cold-active beta-galactosidase from Arthrobacter psychrolactophilus strain F2.
abstract: In this study, we purified and molecularly characterized a cold-active beta-galactosidase from Arthrobacter psychrolactophilus strain F2. The purified beta-galactosidase from strain F2 exhibited high activity at 0 degrees C, and its optimum temperature and pH were 10 degrees C and 8.0, respectively. It was possible to inactivate the beta-galactosidase rapidly at 45 degrees C in 5 min. The enzyme was able to hydrolyze lactose as a substrate, as well as o-nitrophenyl-beta-D-galactopyranoside (ONPG), the Km values with ONPG and lactose being calculated to be 2.8 mM and 50 mM, respectively, at 10 degrees C. Moreover, the bglA gene encoding the beta-galactosidase of strain F2 was cloned and analyzed. The bglA gene consists of a 3,084-bp open reading frame corresponding to a protein of 1,028 amino acid residues. BglAp, the gene product derived from bglA, had several conserved regions for glycosyl hydrolase family 2, e.g., the glycosyl hydrolase 2 (GH2) sugar binding domain, GH2 acid-base catalyst, GH2 triosephosphate isomerase barrel domain, GH2 signature 1, and several other GH2 conserved regions. From these facts, we conclude that the beta-galactosidase from A. psychrolactophilus strain F2, which is a new member of glycosyl hydrolase family 2, is a cold-active enzyme that is extremely heat labile and could have advantageous applications in the food industry.
authors.affiliation: Department of Food Science and Technology,Faculty of Bioindustry, Tokyo University of Agriculture, 196 Yasaka, Abashiri, Hokkaido 099-2493, Japan. t-nakaga@bioindustry.nodai.ac.jp
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Nakagawa
authors.forename: Yuji
authors.initials: Y
authors.lastname: Fujimoto
authors.forename: Ryoko
authors.initials: R
authors.lastname: Ikehata
authors.forename: Tatsuro
authors.initials: T
authors.lastname: Miyaji
authors.forename: Noboru
authors.initials: N
authors.lastname: Tomizuka
mesh_terms: D000595:Amino Acid Sequence; D001173:Arthrobacter / Q000201:enzymology* / Q000235:genetics*; D003080:Cold Temperature; D004795:Enzyme Stability; D008969:Molecular Sequence Data; D001616:beta-Galactosidase / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism
chemical_list: D001616:beta-Galactosidase