• Journal of Microbiology
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• v.42 no.3
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• pp.223-227
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• 2004

An ${\alpha}$-glucosidase inhibitor, SKG-3, was isolated from the fruiting bodies of Ganoderma lucidum and its physico-chemical properties were characterized. It was a highly specific and effective reversible inhibitor of ${\alpha}$-glucosidase. It showed very potent inhibitory activity against a-glucosidase with an IC$\sub$50/ value of 4.6$\mu\textrm{g}$/$m\ell$, but no activity for any other glycosidases tested. Enzyme activity could be recovered upon dialysis, thus providing evidence for the reversibility of the inhibition. A Lineweaver-Burk plot indicated that the SKG-3 inhibition of ${\alpha}$-glucosidase was competitive.

• Biomolecules & Therapeutics
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• v.13 no.1
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• pp.32-34
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• 2005

Effect of isoliquiritigenin isolated from the heartwood of Dalbergia odorifera T. Chen (Leguminosae) on mushroom tyrosinase activity was investigated in vitro using L-tyrosine and L-3, 4-dihydroxyphenylalanine (L-DOPA) as the substrates. When L-tyrosine was used as a substrate, both isoliquiritigenin and kojic acid, a positive control, inhibited tyrosinase activity in a concentration-dependent manner. IC$_{50}$ values of isoliquiritigenin and kojic acid were 61.4 and 52.2 ${\muM}$, respectively. However, isoliquiritigenin showed week inhibitory effect on the oxidation of L-DOPA by tyrosinase with inhibition ratio of 9.1 ${\pm}$ 7.1% at 100 ${\muM}$. It is also suggested that 3-unsubstituted and 4-hydroxyl phenyl group in isoliquiritigenin plays an important role on the inhibition of tyrosinase activity when L-tyrosine was used as a substrate. Analysis of Lineweaver-Burk plot showed that isoliquiritigenin acts as a competitive inhibitor in case of L-tyrosine as a substrate.

• Journal of Microbiology and Biotechnology
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• v.16 no.12
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• pp.1977-1983
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• 2006

Kaempferol was isolated and identified from the methanol extract of the flowers of Impatiens balsamina. Kaempferol showed inhibitory activity against mushroom tyrosinase with an $ID_{50}$ of 0.042 mM. Inhibition kinetics, as determined using a Lineweaver-Burk plot, showed kaempferol to be a competitive inhibitor of mushroom tyrosinase with a $K_i$ value of 0.011 mM. The lag phase of tyrosine hydroxylation catalyzed by mushroom tyrosinase clearly increased on increasing the concentration of kaempferol. In addition to its tyrosinase inhibiting activity, kaempferol strongly inhibited melanin production by Streptomyces bikiniensis, in a dose-dependent manner, without inhibiting cell growth. For comparative purposes, the tyrosinase inhibitory activity of kaempferol was also assayed versus quercetin, a positive standard.

• Journal of Microbiology and Biotechnology
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• v.25 no.2
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• pp.174-177
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• 2015

A potent α-glucosidase inhibitor (compound I) was isolated from coffee brews by activity-based fractionation and identified as a β-carboline alkaloid norharman (9H-pyrido[3.4-b]indole) on the basis of mass spectroscopy and nuclear magnetic resonance spectra (¹H NMR, ¹³C NMR, and COSY). The norharman showed potent inhibition against α-glucosidase enzyme in a concentration-dependent manner, with an IC₅₀ value of 0.27 mM for maltase and 0.41 mM for sucrase. A Lineweaver-Burk plot revealed that norharman inhibited α-glucosidase enzyme uncompetitively, with a K_i value of 0.13 mM.

• Journal of Microbiology and Biotechnology
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• v.20 no.11
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• pp.1521-1523
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• 2010

Bioassay-guided fractionation of a methanol extract of Ganoderma lucidum gave a pure cholesterol esterase inhibitor. On the basis of spectroscopic analysis and comparison with data from the literature, the structure of this compound was identified as $5{\alpha},8{\alpha}$-epidioxyergosta-6,22-dien-$3{\bet}$-ol (compound I). This compound inhibited cholesterol esterase activity with an $IC_{50}$ value of $42{\mu}M$. Lineweaver-Burk plot analysis revealed that compound I is a noncompetitive inhibitor. The findings of this study suggest that compound I may be the active principle of the hypocholesterolemic effect of Ganoderma lucidum.

• Natural Product Sciences
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• v.11 no.2
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• pp.89-91
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• 2005

Effect of the neolignans, honokiol (1) and magnolol (2), isolated from Magnoliae Cortex on mushroom tyrosinase activity was investigated in vitro using L-tyrosine as a substrate. Honokiol (1) inhibited tyrosinase activity significantly in a concentration-dependent manner, on the other hand, magnolol (2) did not show tyrosinase inhibitory effect. Honokiol exhibited tyrosinase inhibitory effect with $IC_{50}$ value of $67.9\;{\mu}M$, and proved to act as a non-competitive inhibitor by the analysis of Lineweaver-Burk plot.

• Journal of Plant Biology
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• v.30 no.4
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• pp.249-255
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• 1987

The effect of polyamine and Ca2+ on D-glucose-6-phosphate cyclohydrolase activity was studied in Daucus carota root. The enzyme activity was reduced in response to increase in concentration of Ca2+, not the Ca2+-calmodulin complex. The inhibition effect due to Ca2+ was reversed by polyamine, especially remarkable at low concentration of Ca2+. The effect of the Ca2+ on the enzyme seemed to compete with polyamine according to the Lineweaver-Burk plot. The enzyme activity from carrot root protoplast cultured in the prescence of verapamil was higher than that of the control. Such cumulative results suggest that the inhibition by the Ca2+ and enhancement or reversal by polyamine could regulate the biosynthesis of pectin and hemicellulose to some extent.

• Archives of Pharmacal Research
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• v.28 no.4
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• pp.400-404
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• 2005

Activity-guided fractionation of a hexane-soluble extract of the roots of Lithospermum erythrorhizon, using a mouse brain monoamine oxidase (MAO) inhibition assay, led to the isolation of two known naphthoquinones, acetylshikonin and shikonin, and a furylhydroquinone, shikonofuran E. These compounds were shown to inhibit MAO with $IC_{50}$ values of 10.0, 13.3, and $59.1 {\mu}M$, respectively. Although no specificity for MAO-A and MAO-B was shown by acetylshikonin and shikonin, a Lineweaver-Burk plot analysis indicated that the inhibition was competitive for both MAO-A and MAO-B activity.

• Analytical Science and Technology
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• v.20 no.1
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• pp.49-54
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• 2007

For the practical use as a biosensor, a rubber electrode bound by polybutadiene was newly devised for the determination of hydrogen peroxide. Then its electrochemical behaviors were investigated. The signal could be obtained at low electrode potential between 0.0 ~ -0.5 V (vs. Ag/AgCl) with a detection limit of $1.4{\times}10^{-4}M$ and its potential dependence was linear in the experimental range. Especially its Lineweaver-Burk plot showed a very good linearity giving the evidence of a good enzyme immobilization on the surface of the electrode. And mechanical stability of the electrode resulted from using rubber binder presented a new possibility for the practical use of biosensor.

• Microbiology and Biotechnology Letters
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• v.18 no.5
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• pp.496-500
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• 1990

When pepsin was used at a concentration of 8 mglml for hydrolysis of 0.02% casein, inhibitory activity of this inhibitor was proportional to a inhibitor concentration of 20 ${\mu}g$/ml, and fifty percent inhibition ($IC_{50}$) was observed to be 15 ${\mu}g$/ml. The inhibitor was pH-stable at pH range of 5-9 at $100^{\circ}C$ for 10 minutes and thermo-stable at pH 7.0 at $100^{\circ}C$ to give 100% activity for 20 minutes. The formation of pepsin-inhibitor complex was confirmed by sephadex 6-25 gel filtration and type of inhibition was determined as non-competitive inhibition by Lineweaver-Burk plot. The inhibitor strongly inhibited acid proteases such as pepsin and renin, and it was soluble in methanol very well. On TLC analysis of silicagel 60 using various sohent systems, the inhibitor gave a single spot at Rf range 0.4-0.6. From the result of IR spectrum and color reaction (Rydon-Smith, Biuret), this inhibitor was considered as peptide substance. Melting point and elemental contents were 220-$230^{\circ}C$, and C 50.61%-H 8.02%-N 9.34% (found), respectively.