Wyniki wyszukiwania

1

Indirect inactivation of tyrosinase in its action on tyrosine

100%

Munoz-Munoz J. L., Garcia-Molina F., Acosta-Motos J. R., Arribas E., Garcia-Ruiz P. A., Tudela J., Garcia-Canovas F., Rodriguez-Lopez J. N.

Acta Biochimica Polonica

|

2011

|

tom 58

|

nr 4

Under aerobic conditions, tyrosinase is inactivated by dopa as a result of suicide inactivation, and, under anaerobic conditions, as a result of irreversible inactivation. However, tyrosine protects the enzyme from being inactivated by dopa under anaerobic conditions. This paper describes how under aerobic conditions the enzyme acting on tyrosine is not directly inactivated but undergoes a process of indirect suicide inactivation provoked by reaction with the o-diphenol originated from the evolution of o-dopaquinone and accumulated in the reaction medium.

2

Kinetic cooperativity of tyrosinase. A general mechanism

100%

Munoz-Munoz J. L., Garcia-Molina F., Varon R., Tudela J., Garcia-Canovas F., Rodriguez-Lopez J. N.

Acta Biochimica Polonica

|

2011

|

tom 58

|

nr 3

Tyrosinase shows kinetic cooperativity in its action on o-diphenols, but not when it acts on monophenols, confirming that the slow step is the hydroxylation of monophenols to o-diphenols. This model can be generalised to a wide range of substrates; for example, type SA substrates, which give rise to a stable product as the o-quinone evolves by means of a first or pseudo first order reaction (α-methyl dopa, dopa methyl ester, dopamine, 3,4-dihydroxyphenylpropionic acid, 3,4-dihydroxyphenylacetic acid, α-methyl-tyrosine, tyrosine methyl ester, tyramine, 4-hydroxyphenylpropionic acid and 4-hydroxyphenylacetic acid), type SB substrates, which include those whose o-quinone evolves with no clear stoichiometry (catechol, 4-methylcatechol, phenol and p-cresol) and, lastly, type SC substrates, which give rise to stable o-quinones (4-tert-butylcatechol/4-tert-butylphenol).

3

The role of alkyl chain length in the inhibitory effect n-alkyl xanthates on mushroom tyrosinase activities

84%

Saboury A. A., Alijanianzadeh M., Mansoori-Torshizi H.

Acta Biochimica Polonica

|

2007

|

tom 54

|

nr 1

Sodium salts of four n-alkyl xanthate compounds, C2H5OCS2Na (I), C3H7OCS2Na (II), C4H9OCS2Na (III), and C6H13OCS2Na (IV) were synthesized and examined for inhibition of both cresolase and catecholase activities of mushroom tyrosinase (MT) in 10 mM sodium phosphate buffer, pH 6.8, at 293 K using UV spectrophotemetry. 4-[(4-methylbenzo)azo]-1,2-benzendiol (MeBACat) and 4-[(4-methylphenyl)azo]-phenol (MePAPh) were used as synthetic substrates for the enzyme for catecholase and cresolase reactions, respectively. Lineweaver-Burk plots showed different patterns of mixed, competitive or uncompetitive inhibition for the four xanthates. For the cresolase activity, I and II showed uncompetitive inhibition but III and IV showed competitive inhibition pattern. For the catecholase activity, I and II showed mixed inhibition but III and IV showed competitive inhibition. The synthesized compounds can be classified as potent inhibitors of MT due to their Ki values of 13.8, 11, 8 and 5 μM for the cresolase activity, and 1.4, 5, 13 and 25 μM for the catecholase activity for I, II, III and IV, respectively. For the catecholase activity both substrate and inhibitor can be bound to the enzyme with negative cooperativity between the binding sites (α > 1) and this negative cooperativity increases with increasing length of the aliphatic tail of these compounds. The length of the hydrophobic tail of the xanthates has a stronger effect on the Ki values for catecholase inhibition than for cresolase inhibition. Increasing the length of the hydrophobic tail leads to a decrease of the Ki values for cresolase inhibition and an increase of the Ki values for catecholase inhibition.

4

The effect of chemo- and chemoimmunotherapy on the presence of circulating melanoma cells in peripheral blood. Preliminary results

84%

Szenajch J., Kozak A., Kruszewski A. A., Babiej E., Chomicka M., Struzyna J., Wiktor-Jedrzejczak W.

Acta Biochimica Polonica

|

1998

|

tom 45

|

nr 1

Reverse transcription and polymerase chain reaction (RT/PCR) with primers specific for tyrosinase allow for a new method of early detection of individual melanoma cells in peripheral blood. Using this test the effect of chemo- and chemoimmunotherapy on the spread of early micrometastatic cancer cells has been evaluated. No significant correlations have been found between RT/PCR results on the one hand and stage of disease, a kind of the therapy protocol used and usage of the therapy as an adjuvant or palliative on the other hand. Thus, although the RT/PCR test for detection of circulating individual melanoma cells might help in identification of minimal residual disease in some patients, it has no application for routine staging of more advanced disease and in monitoring the response to therapy.

5

Artykuł dostępny w postaci pełnego tekstu - kliknij by otworzyć plik

The biological activities of troponoids and their use in agriculture. A review

67%

Saniewski M., Horbowicz M., Kanlayanarat S.

Journal of Horticultural Research

|

2014

|

tom 22

|

nr 1

6

Evaluation of melanogenesis in A-375 melanoma cells treated with 5,7-dimethoxycoumarin and valproic acid

67%

Chodurek E., Orchel A., Orchel J., Kurkiewicz S., Gawlik N., Dzierzewicz Z., Stepien K.

Cellular and Molecular Biology Letters

|

2012

|

tom 17

|

nr 4

Malignant melanoma (melanoma malignum) is one of the most dangerous types of tumor. It is very difficult to cure. In recent years, a lot of attention has been given to chemoprevention. This method uses natural and synthetic compounds to interfere with and inhibit the process of carcinogenesis. In this study, a new treatment strategy was proposed consisting of a combination of 5,7-dimethoxycoumarin (DMC), an activator of melanogenesis, and valproic acid (VPA), a well-known drug that is one of the histone deacetylase inhibitors (HDACis). In conjunction with 1 mM VPA, all of the tested concentrations of DMC (10–150 μM) significantly decreased the proliferation of A-375 cells. VPA and DMC also induced the synthesis of melanin and the formation of dendrite and star-shaped cells. Tyrosinase gene expression and tyrosinase activity significantly increased in response to VPA treatment. Pyrolysis with gas chromatography and mass spectrometry (Py-GC/MS) was used to investigate the structure of the isolated melanin. This showed that the quantitative and qualitative components of melanin degradation products are dependent on the type of applied melanogenesis inductor. Products derived from eumelanin were detected in the pyrolytic profile of melanin isolated from A-375 cells stimulated with DMC. Thermal degradation of melanin isolated from melanoma cells after exposure to VPA or a mixture of VPA and DMC revealed the additional presence of products derived from pheomelanin.

7

Effects of juglone on growth of cucumber seedlings with respect to physiological and anatomical parameters

59%

Terzi I., Kocacaliskan I., Benlioglu O., Solak K.

Acta Physiologiae Plantarum

|

2003

|

tom 25

|

nr 4

Ograniczanie wyników

Indirect inactivation of tyrosinase in its action on tyrosine

Kinetic cooperativity of tyrosinase. A general mechanism

The role of alkyl chain length in the inhibitory effect n-alkyl xanthates on mushroom tyrosinase activities

The effect of chemo- and chemoimmunotherapy on the presence of circulating melanoma cells in peripheral blood. Preliminary results

The biological activities of troponoids and their use in agriculture. A review

Evaluation of melanogenesis in A-375 melanoma cells treated with 5,7-dimethoxycoumarin and valproic acid

Effects of juglone on growth of cucumber seedlings with respect to physiological and anatomical parameters