Biomedical subjects

Tzong-Huei Lee

Publications and source records attributed to Tzong-Huei Lee.

11 recordsLinked to original sources

PubMed2026

Structural Characterization and Engineering of a GH134 β-Mannanase from Aspergillus nidulans for Enhancement of Activity and Stability.

Mannans are abundant plant hemicelluloses, and endo-β-mannanases are important biocatalysts for their conversion into functional manno-oligosaccharides. Here, we report the structural and functional characterization of a glycoside hydrolase family 134 β-mannanase from Aspergillus nidulans (AnGH134) and a structure-guided engineering strategy to improve its performance on locust bean gum. The 1.75 Å crystal structure reveals the conserved lysozyme-like fold of GH134 enzymes and supports an inverting catalytic mechanism with Glu43 and Asp55 as the putative catalytic residues. Docking, mutational, and molecular dynamics analyses indicate that AnGH134 uses an extended substrate-binding groove and that groove-exit residues and the C-terminal region contribute to productive catalysis. Guided by these findings, N-terminal fusion of CBM10 enhanced catalytic efficiency and thermal stability, whereas C-terminal fusion was detrimental. These results provide a framework for engineering GH134 mannanases.

Aspergillus nidulans↗

PubMed2006

Potential of a simple solid-phase extraction method coupled to analytical and bioanalytical methods for an improved determination of microcystins in algal samples.

Artemia assays and protein phosphatase assays are commonly used for the screening of microcystins (MCs) in algal samples instead of the standard mouse toxicity assay. However, it has been shown that their results are often biased because of the matrix effects. To eliminate the possible interferences in the algal matrices, a new solid-phase extraction (SPE) method using silica gel as a sorbent was developed and evaluated. Results show that this SPE method could not only reduce the toxicity of the Microcystis samples towards brine shrimp by 50-80% but also eliminate 90-100% of the endogenous phosphatase activity from Spirulina and Chlorella samples, thus improving the determination of microcystins in algal samples using either of the two bioanalytical methods. The application of this SPE method as an off-line cleanup for high-performance liquid chromatography (HPLC) with UV detection is also described in this study. After SPE, the HPLC chromatograms of Microcystis samples have clear baselines that have no interferences with the analyte peaks.

Animals↗

PubMed2006

Comparison of protein phosphatase inhibition activities and mouse toxicities of microcystins.

Eight naturally purified microcystins (MCs), including MC-LR, -FR, -WR, -RR, [d-Asp(3)]MC-FR, -WR, -RR, and [Dha(7)]MC-RR were utilized to determine the effects of amino acid substitutions and modifications on MC-induced protein phosphatase inhibition activity and mouse toxicity. Catalytic subunits of protein phosphatase 1 (PP-1) and 2A (PP-2A) were purified and subjected to the inhibition assays, and intraperitoneal injection was used to administer MCs into mice for the toxicity assay. It is found that the replacement of the non-polar amino acid l-leucine at the second position of these heptacyclic peptide toxins by a polar l-arginine reduces their mouse toxicities and inhibitory activities against PP-1 and PP-2A to different extends. Demethylation of methyldehydroalanine (Mdha) at the seventh amino acid of MC-RR exhibits the least mouse toxicity and phosphatase inhibition. The loss of a methyl group on the common methylaspartic acid (MeAsp) at the third position of MC-FR, -WR, and -RR does not alter their toxicity levels, but dominantly reduces their activities in PP-1 inhibition compared to other substitutions or modifications. This suggests that the methyl group on MeAsp is also important for MCs inhibition. However, such a tendency is not observed for PP-2A. By comparing the LD(50) values of the mouse toxicity assay and IC(50) values of the PP-1 and PP-2A inhibition assay of eight MCs using linear regression, it is evident that the MC-induced toxicity is much more related to the inhibition of PP-2A than PP-1, which suggests that PP-2A inhibition may play a major role in the MC-induced mouse toxicity.

Animals↗

PubMed2006

A new gamma-lactone from the leaves of Cinnamomum kotoense.

A new C19 gamma-lactone, cinnakotolactone (1), along with a known analogue, isolinderanolide B (2), were isolated from the n-hexane layer of the leaf extracts of Cinnamomum kotoense. Their structures were elucidated on the basis of spectroscopic analysis. The anti-proliferation activities of 1 and 2 were evaluated against human HT29 and MCF-7 cancer cell lines, and their IC50 values ranged from 3.3 +/- 0.3 to 25.8 +/- 5.3 microM.

Cell Proliferation↗

PubMed2006

New constituents from the heartwood of Picea morrisonicola HAYATA.

Three new constituents, including a p-menthane type monoterpene, trans-p-menthane-7,8,9-triol (1), an aromatic, 2,6-dihydroxy-3,4-dimethylbenzoic acid methyl ester (2), and a lignan, (+)-morrisonicolanin (3), were isolated from the low polar layer of heartwood extracts of Picea morrisonicola, and their structures were elucidated on the basis of spectroscopic analysis. Of these compounds identified, 1 was obtained as its diacetylated derivative 1a, and 2 was the chemical entity first isolated from a natural source.

Benzoates↗

PubMed2005

Prorocentin, a new polyketide from the marine dinoflagellate Prorocentrum lima.

Prorocentin (1), isolated from an okadaic acid-producing organism, Prorocentrum lima, possessed all-trans trienes, an epoxide, as well as the 6/6/6-trans-fused/spiro-linked polyether ring moieties. The unique structure supports the proposed cyclization mechanism, polyene formation, epoxidation, and cyclization, of marine polyether toxins. The relative stereostructure was determined on the basis of spectral data. [structure: see text]

Animals↗

PubMed2005

Furocoumarin glycosides from the leaves of Ficus ruficaulis Merr. var. antaoensis.

From the methanolic extract of the leaves of Ficus ruficaulis Merr. var. antaoensis, 5-O-beta-D-glucopyranosyl-6-hydroxyangelicin (1), 6-O-beta-D-glucopyranosyl-5-hydroxyangelicin (2), 5,6-O-beta-D-diglucopyranosylangelicin (3), 8-O-beta-D-glucopyranosyl-5-hydroxypsoralen (4), 5-O-beta-D-glucopyranosyl-8-hydroxypsoralen (5), 3,4,5-trihydroxydehydro-alpha-ionol-9-O-beta-D-glucopyranoside (6), rutin (7), and isoquercitrin (8) were isolated. The structures of compounds 1-4 were elucidated by the analysis of their spectroscopic data. Their in vitro antiproliferation activities were also evaluated.

Antineoplastic Agents, Phytogenic↗

PubMed2005

Inhibitory effects of acylated kaempferol glycosides from the leaves of Cinnamomum kotoense on the proliferation of human peripheral blood mononuclear cells.

A new chemical entity, namely kaempferol 3- O-alpha-L-[2-(Z)-p-coumaroyl-4-(E)-p-coumaroyl]rhamnopyranoside (1), and the known kaempferol 3-O-alpha-L-[2,4-di-(E)-p-coumaroyl]rhamnopyranoside (2) have been isolated from the methanolic extract of leaves of Cinnamomum kotoense. Structural elucidation of compounds 1 and 2 were achieved on the basis of spectroscopic analysis. The effects of compounds 1 and 2 on phytohemagglutinin (PHA) stimulated cell proliferation were studied towards human peripheral blood mononuclear cells (PBMC). The results indicated that compounds 1 and 2 suppressed PBMC proliferation induced by PHA with an IC50 value of 5.0 +/- 1.3 and 6.0 +/- 1.5 microM, respectively. Interleukin-2 production in activated PBMC inhibited by compounds 1 and 2 were in a concentration-dependent manner. Therefore, we suggested that compounds 1 and 2 in C. kotoense were likely the growth modulators for PBMC.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed2002

Five new phenolics from the roots of Ficus beecheyana.

From the ethanolic extract of the roots of Ficus beecheyana, threo-2,3-bis(4-hydroxy-3-methoxyphenyl)-3-ethoxypropan-1-ol (1), erythro-2,3-bis(4-hydroxy-3-methoxyphenyl)-3-ethoxypropan-1-ol (2), trans-4,5-bis(4-hydroxy-3-methoxyphenyl)-1,3-dioxacyclohexane (3), threo-3-(4-hydroxy-3,5-dimethoxyphenyl)-3-ethoxypropane-1,2-diol (4), 2,3-dihydroxy-1-(4-hydroxy-3,5-dimethoxyphenyl)-1-propanone (5), and 3-hydroxy-1-(4-hydroxy-3,5-dimethoxyphenyl)-1-propanone (6) were isolated. The structures of the new compounds 1-5 were elucidated by the analysis of their spectroscopic data.

Ficus↗

PubMed2002

Inhibitory effects of glycosides from the leaves of Melaleuca quinquenervia on vascular contraction of rats.

Two new glycosides, 3-hydroxy-5-methoxy-4-methylphenyl beta-D-glucopyranoside (1) and 4-benzoyl-2-C-beta-glucopyranosyl-3,5-dihydroxy-6-methylphenyl beta-D-glucopyranoside (2), together with four known glycosides, 2-endo-beta-D-glucopyranosyloxy-1,8-cineole (3a), 2-exo-beta-D-glucopyranosyloxy-1,8-cineole (3b), roseoside (4), and citroside A (5), were isolated from the methanolic extract of leaves of Melaleuca quinquenervia. Their structures were elucidated on the basis of spectroscopic analysis. Compounds 1, 2a and 3 inhibited contractile response induced by phenylephrine in aortic rings from Sprague-Dawley rats. This inhibition was independent of the endothelium. Compounds 2 and 4 significantly relaxed precontracted aortic rings, in an endothelium-dependent manner. Pretreatment of N(omega)-nitro-L-arginine (L-NNA), a nitric oxide synthase inhibitor, partially attenuated the vasorelaxation induced by both compounds, suggesting that nitric oxide was likely the responsible mediator. The rank-order potency (EC 50 value) of vasorelaxing activities of these compounds is 4 > 2 > 2a > 3 > 1.

Animals↗

PubMed2002

Detection of tetrodotoxin by HPLC in shellfishes and goby from south Taiwan.

High performance liquid chromatography (HPLC) using fluorescent detection following post-column alkaline degradation and a sample preparation procedure for the analysis were established to detect tetrodotoxins (TTXs) in seafood. In south Taiwan Prefectures, each specimen of shellfishes and gobies, collected from Chiayi, Tainan, and Pingtung from January 1997 to May 1998, was analyzed by HPLC to detect the presence and quantity of TTXs. Overall results showed that only 5 specimens out of 557 specimens contained TTXs; the toxic species were gastropod Natica lineata and Nassarius livescens. The highest TTX content is 10.0 microg/g in N. livescens. Gobies and other species of shellfishes were nontoxic. Although the rate of toxic specimens in all samples was low and showed no seasonal trends, the TTX contents of toxic specimens were higher than safety criteria value.

Animals↗