Results found: 3

Number of results on page

Search results

Search:
in the keywords: tyrosinase

Sort By:

Limit search:

Kinetic cooperativity of tyrosinase. A general mechanism

100%

Muñoz-Muñoz J. L., Garcia-Molina F., Varon R., Tudela J., Garcia-Cánovas F., Rodríguez-López J. N.

Acta Biochimica Polonica

2011

vol. 58

issue 3

303-311

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).

Indirect inactivation of tyrosinase in its action on tyrosine

70%

Muñoz-Muñoz J. L., Garcia-Molina F., Acosta-Motos J. R., Arribas E., Garcia-Ruíz P. A., Tudela J., Garcia-Cánovas F., Rodríguez-López J. N.

Acta Biochimica Polonica

2011

vol. 58

issue 4

477-488

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.

A Critical View on the Phenol Index as a Measure of Phenol Compounds Content in Waters. Application of a Biosensor

51%

Kochana J., Adamski J., Parczewski A.

Ecological Chemistry and Engineering S

2012

vol. 19

issue 3

383-391

Phenol index is considered as an important indicator of water purity and quality. Usually phenol index is determined by a spectrophotometric method the calibration being based on phenol standards. Unfortunately, the absorptivities of different phenols compounds differ from each other. This leads to significant uncertainty concerning content of phenols in water. It is shown that the same shortage of the phenol index appears also if it is determined using an amperometric biosensor based on tyrosinase. The sensitivity of the biosensor response to four phenol compounds: phenol, catechol, 3-cresol and 4-chlorophenol was examined, as well as possible interactions between phenols, according to 24 factorial experiment. It was proved that individual phenols affect phenol index independently from each other, ie no significant interaction between phenols was detected. However, sensitivity of the biosensor to different phenols is not the same. Relationship between phenol index and concentrations of phenols in water is discussed.

Indeks fenolowy jest ważnym wskaźnikiem czystości i jakości wody. Oznacza się go zwykle metodami spektrofotometrycznymi z 4-aminoantypiryną, stosując fenol jako wzorzec. Ponieważ współczynniki absorpcji różnych związków fenolowych różnią się, wyznaczona wartość indeksu fenolowego obarczona jest znaczną niepewnością. Podobny efekt występuje, gdy indeks fenolowy oznaczany jest przy użyciu biosensora amperometrycznego opartego na tyrozynazie. W pracy wyznaczono czułości biosensora w stosunku do czterech związków fenolowych: fenolu, katecholu, 3-krezolu oraz 4-chlorofenolu oraz zbadano możliwe interakcje pomiędzy fenolami. Doświadczenia prowadzono według planów czynnikowych 24. Wykazano, że poszczególne fenole wpływają na indeks fenolowy niezależnie od siebie, tzn. nie stwierdzono istotnych interakcji pomiędzy fenolami. Jednak czułość biosensora jest różna w stosunku do różnych fenoli. Przedyskutowano zależność pomiędzy indeksem fenolowym a stężeniami fenoli w wodzie.

Refine search results

2 Acta Biochimica Polonica

1 Ecological Chemistry and Engineering S

1 2012

2 2011

2 Garcia-Cánovas F.

2 Garcia-Molina F.

2 Muñoz-Muñoz J. L.

2 Rodríguez-López J. N.

2 Tudela J.

1 Acosta-Motos J. R.

1 Adamski J.

1 Arribas E.

1 Garcia-Ruíz P. A.

1 Kochana J.

1 Parczewski A.

1 Varon R.

Search results

Kinetic cooperativity of tyrosinase. A general mechanism

Indirect inactivation of tyrosinase in its action on tyrosine

A Critical View on the Phenol Index as a Measure of Phenol Compounds Content in Waters. Application of a Biosensor