Kinetic study of monophenol and o-diphenol binding to oxytyrosinase |
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Authors: | F García-Molina MJ Pealver LG Fenoll JN Rodríguez-Lpez R Varn F García-Cnovas J Tudela |
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Institution: | aGrupo de Investigación de Enzimología (GENZ), Departamento de Bioquímica y Biología Molecular-A, Facultad de Biología, Universidad de Murcia, A. Correos 4021, E-30080, Murcia, Spain bDepartamento de Química-Física, Escuela Politécnica Superior de Albacete, Universidad de Castilla La Mancha, E-02071 Albacete, Spain |
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Abstract: | The complex reaction mechanism of tyrosinase involves three enzymatic forms, two overlapping catalytic cycles and a dead-end complex. The deoxytyrosinase form binds oxygen with a high degree of affinity, μM. The mettyrosinase and oxytyrosinase forms bind monophenols and o-diphenols, although the former is inactive on monophenols. Analytical expressions for the catalytic and Michaelis constants of tyrosinase towards phenols and o-diphenols have been derived. Thus, the Michaelis constant of tyrosinase towards monophenols and o-diphenols are related with the catalytic constants for monophenols and o-diphenols , respectively, and with the binding rate constants of the oxytyrosinase form with these substrates (k+4 and k+6, respectively), by means of the expressions and . From these expressions, we calculate the values of the binding rate constant of oxytyrosinase to the substrates (monophenols and o-diphenols) for tyrosinases from different biological sources, and reveal that the o-diphenols bind more rapidly to oxytyrosinase than the monophenols. In addition, a new kinetic constant (the Michaelis constant for o-diphenol in the monophenolase activity), is derived and determined. Thus, it has been shown that tyrosinase has apparently higher affinity towards o-diphenols in its monophenolase than in its diphenolase activity. |
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Keywords: | Monophenol and o-diphenol Oxytyrosinase Dead-end complex |
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