title: Purification and characterization of a beta-glucosidase from Citrus sinensis var. Valencia fruit tissue.
abstract: A preliminary survey demonstrated activity for alpha-D-glucosidase, alpha-D-mannosidase, alpha-L-arabinosidase, beta-D-glucosidase, beta-D-xylosidase, and beta-D-galactosidase in orange fruit flavedo and albedo tissue. alpha-L-Rhamnosidase was not detected. Subsequently, a beta-glucosidase was purified from mature fruit rag tissue (composed of intersegmental septa, squeezed juice sacs, and fruit core tissue) of Citrus sinensis var. Valencia. The beta-glucosidase exhibited low levels of activity against p-nitrophenyl-beta-D-fucopyranoside (13.5%) and p-nitrophenyl-alpha-D-glucopyranoside (7.0%), compared to its activity against p-nitrophenyl-beta-D-glucopyranoside (pNPG, 100%). The enzyme was purified by a combination of ion exchange (anion and cation) and gel filtration (Superdex and Toyopearl HW-55S) chromatography. It has an apparent molecular mass of 64 kDa by denaturing electrophoresis or 55 kDa by gel filtration chromatography (BioGel P-100). Hydrolysis of pNPG demonstrated a pH optimum between 4.5 and 5.5. At pH 5.0 the temperature optimum was 40 degrees C. At pH 5.0 and 40 degrees C the K(m) for pNPG was 0.1146 mM and it had a V(max) of 5.2792 nkatal x mg(-1) protein (katal = 0.06 International Units = the amount of enzyme that produces, under standard conditions, one micromol of product per min). Of the substrates tested, the enzyme was most active against the disaccharide cellobiose (1-->4), but was not active against p-nitrophenyl-beta-D-cellobioside. High levels of activity also were observed with the disaccharides laminaribiose (1-->3), gentiobiose (1-->6), and sophorose (1-->2). Activity greater than that observed with pNPG was obtained with the flavonoids hesperetin-7-glucoside and prunin (naringenin-7-glucoside), salicin, mandelonitrile-beta-D-glucoside (a cyanogenic substrate), and sinigrin (a glucosinolate). The enzyme was not active against amygdalin, coniferin, or limonin glucoside.
authors.affiliation: Citrus and Subtropical Products Laboratory, Agricultural Research Service, U.S. Department of Agriculture, 600 Avenue S, NW, Winter Haven, Florida 33881, USA. rcameron@citrus.usda.gov
authors.forename: R G
authors.initials: RG
authors.lastname: Cameron
authors.forename: J A
authors.initials: JA
authors.lastname: Manthey
authors.forename: R A
authors.initials: RA
authors.lastname: Baker
authors.forename: K
authors.initials: K
authors.lastname: Grohmann
mesh_terms: D002850:Chromatography, Gel; D002957:Citrus / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D008970:Molecular Weight; D013696:Temperature; D001617:beta-Glucosidase / Q000302:isolation & purification* / Q000378:metabolism*
chemical_list: D001617:beta-Glucosidase