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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).

Kinetic analysis of the transient phase and steady state of open multicyclic enzyme cascades

100%

Varon R., Havsteen B. H., Valero E., Molina-Alarcon M., Garcia-Canovas F., Garcia-Moreno M.

Acta Biochimica Polonica

2005

tom 52

nr 4

This paper presents a kinetic analysis of the whole reaction course, i.e. of both the transient phase and the steady state, of open multicyclic enzyme cascade systems. Equations for fractional modifications are obtained which are valid for the whole reaction course. The steady state expressions for the fractional modifications were derived from the latter equations since they are not restricted to the condition of rapid equilibrium. Finally, the validity of our results is discussed and tested by numerical integration. Apart from the intrinsic value of knowing the kinetic behaviour of any of the species involved in any open multicyclic enzyme cascade, the kinetic analysis presented here can be the basis of future contributions concerning open multicyclic enzyme cascades which require the knowledge of their time course equations (e.g. evaluation of the time needed to reach the steady state, suggestion of kinetic data analysis, etc.), analogous to those already carried out for open bicyclic cascades.

Indirect inactivation of tyrosinase in its action on tyrosine

84%

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.

Ograniczanie wyników

3 Acta Biochimica Polonica

3 Garcia-Canovas F.

2 Garcia-Molina F.

2 Munoz-Munoz J. L.

2 Rodriguez-Lopez J. N.

2 Tudela J.

2 Varon R.

1 Acosta-Motos J. R.

1 Arribas E.

1 Garcia-Moreno M.

1 Garcia-Ruiz P. A.

1 Havsteen B. H.

1 Molina-Alarcon M.

1 Valero E.

2 2011

1 2005

Wyniki wyszukiwania

Kinetic cooperativity of tyrosinase. A general mechanism

Kinetic analysis of the transient phase and steady state of open multicyclic enzyme cascades

Indirect inactivation of tyrosinase in its action on tyrosine