title: A direct continuous spectrophotometric assay for glycosidases with 3-nitro-2-pyridyl glycosides by tautomerization of 2-hydroxy-3-nitropyridine.
abstract: Two kinds of 3-nitro-2-pyridyl glycosides were synthesized and evaluated as substrates for continuous spectrophotometric assay for glycosidases. The liberated aglycon, 2-hydroxy-3-nitropyridine, immediately tautomerized to 3-nitro-2(1H)-pyridone, causing an absorption shift of ca. 60 nm even under acidic conditions (pH 3-6). Consequently, the enzymatic hydrolysis of these glycosides was monitored continuously in the acidic to neutral pH range (pH 4-7), the optimum pH for most glycosidases. The absorbance of liberated aglycon increased linearly at 390 nm until 10% consumption of the substrate to enable the initial rate to be determined at once without terminating the reaction. The kinetic parameters for the hydrolysis of 3-nitro-2-pyridyl glycosides were obtained from the slopes of the progress curves and were compared with those obtained from the conventional discontinuous assay using p- and o-nitrophenyl glycosides as substrates. The kinetic parameters indicated that 3-nitro-2-pyridyl glycosides were more activated and specific substrates, but with less affinity to the enzymes than the corresponding nitrophenyl glycosides. Moreover, the absorbance shift by tautomerization should promise further applications to continuous spectrophotometric assays for other enzymes acting under acidic conditions, such as acid proteases and acid phosphatases.
authors.affiliation: Institute for Chemical Research, Kyoto University, Uji, 611-0011, Japan.
authors.forename: Seung-Jin
authors.initials: SJ
authors.lastname: Ma
authors.forename: Jun
authors.initials: J
authors.lastname: Hiratake
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Nakai
authors.forename: Minoru
authors.initials: M
authors.lastname: Izumi
authors.forename: Koichi
authors.initials: K
authors.lastname: Fukase
authors.forename: Shoichi
authors.initials: S
authors.lastname: Kusumoto
authors.forename: Kanzo
authors.initials: K
authors.lastname: Sakata
mesh_terms: D001234:Aspergillus niger / Q000201:enzymology; D006026:Glycoside Hydrolases / Q000032:analysis* / Q000378:metabolism; D007700:Kinetics; D009005:Monosaccharides / Q000378:metabolism*; D011725:Pyridines / Q000378:metabolism*; D011728:Pyridones / Q000737:chemistry / Q000378:metabolism*; D013053:Spectrophotometry / Q000379:methods; D013379:Substrate Specificity
chemical_list: C457780:2-hydroxy-3-nitropyridine; C457779:3-nitro-2-pyridyl glycopyranoside; D009005:Monosaccharides; D011725:Pyridines; D011728:Pyridones; C027829:2-methyl-3-nitro-4-methoxymethyl-5-cyano-6-oxypyridine; D006026:Glycoside Hydrolases