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Seung-Jin Ma

Publications and source records attributed to Seung-Jin Ma.

4 recordsLinked to original sources
PubMed2006

An immunoassay for a urinary metabolite as a biomarker of human exposure to the pyrethroid insecticide permethrin.

Permethrin is the most popular synthetic pyrethroid insecticide used in agriculture and public health. For the assessment of human exposure to permethrin, a competitive indirect enzyme-linked immunosorbent assay (ELISA) for the detection of the glycine conjugate of a major metabolite, cis-/trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane-1-carboxylic acid (DCCA), of permethrin was developed based on a polyclonal antibody. An assay based on an antibody with a high sensitivity was optimized and characterized. The IC50 value and the detection range for trans-DCCA-glycine, in the assay buffer were 1.2 and 0.2-7.0 microg/L, respectively. The antibody recognized trans-DCCA-glycine and the mixture of cis-/trans-DCCA-glycine with an isomer range from 30:70 to 50:50 nearly equally. Little or no cross-reactivity to permethrin and its other free metabolites or glycine conjugates was measured. The integration of the ELISA and solid-phase extraction which was used to reduce the matrix effect from human urine samples provided for analysis of total cis-/trans-DCCA-glycine at low parts per billion levels in the samples. The limit of quantitation of the target analyte was 1.0 microg/L in urine with a limit of detection of 0.1 microg/L in buffer. This assay might be a useful tool for monitoring human exposure to permethrin.

Biomarkers↗
PubMed2002

A direct continuous spectrophotometric assay for glycosidases with 3-nitro-2-pyridyl glycosides by tautomerization of 2-hydroxy-3-nitropyridine.

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.

Aspergillus niger↗
PubMed2002

Cloning of beta-primeverosidase from tea leaves, a key enzyme in tea aroma formation.

A beta-primeverosidase from tea (Camellia sinensis) plants is a unique disaccharide-specific glycosidase, which hydrolyzes aroma precursors of beta-primeverosides (6-O-beta-D-xylopyranosyl-beta-D-glucopyranosides) to liberate various aroma compounds, and the enzyme is deeply concerned with the floral aroma formation in oolong tea and black tea during the manufacturing process. The beta-primeverosidase was purified from fresh leaves of a cultivar for green tea (C. sinensis var sinensis cv Yabukita), and its partial amino acid sequences were determined. The beta-primeverosidase cDNA has been isolated from a cDNA library of cv Yabukita using degenerate oligonucleotide primers. The cDNA insert encodes a polypeptide consisting of an N-terminal signal peptide of 28 amino acid residues and a 479-amino acid mature protein. The beta-primeverosidase protein sequence was 50% to 60% identical to beta-glucosidases from various plants and was classified in a family 1 glycosyl hydrolase. The mature form of the beta-primeverosidase expressed in Escherichia coli was able to hydrolyze beta-primeverosides to liberate a primeverose unit and aglycons, but did not act on 2-phenylethyl beta-D-glucopyranoside. These results indicate that the beta-primeverosidase selectively recognizes the beta-primeverosides as substrates and specifically hydrolyzes the beta-glycosidic bond between the disaccharide and the aglycons. The stereochemistry for enzymatic hydrolysis of 2-phenylethyl beta-primeveroside by the beta-primeverosidase was followed by (1)H-nuclear magnetic resonance spectroscopy, revealing that the enzyme hydrolyzes the beta-primeveroside by a retaining mechanism. The roles of the beta-primeverosidase in the defense mechanism in tea plants and the floral aroma formation during tea manufacturing process are also discussed.

Amino Acid Sequence↗