Considerations about the inhibition of monophenolase and diphenolase activities of tyrosinase. Characterization of the inhibitor concentration which generates 50 % of inhibition, type and inhibition constants. A review

Abstract

Tyrosinase is a copper oxidase enzyme which catalyzes the first two steps in the melanogenesis pathway, L tyrosine to L-dopa conversion and, then, to o-dopaquinone and dopachrome. Hypopigmentation and, above all, hyperpigmentation issues can be originated depending on their activity. This enzyme also promotes the browning of fruits and vegetables. Therefore, control of their activity by regulators is research topic of great relevance. In this work, we consider the use of inhibitors of monophenolase and diphenolase activities of the enzyme in order to accomplish such control. An experimental design and data analysis which allow the accurate calculation of the degree of inhibition of monophenolase activity (iM) and diphenolase activity (iD) are proposed. The IC50 values (amount of inhibitor that causes 50 % inhibition at a fixed substrate concentration) can be calculated for the two activities and from the values of ICM 50 (monophenolase) and ICD 50(diphenolase). Addi tionally, the strength and type of inhibition can be deduced from these values. The data analysis from these ICD 50 values allows to obtain the values of Kapp I1 or Kapp I2 , or Kapp I1 and Kapp I3 from the values of ICM 50. In all cases, the values of the different Kapp I must satisfy their relationship with ICM 50 and ICD 50.