EFFECT OF L-ASCORBIC-ACID ON THE MONOPHENOLASE ACTIVITY OF TYROSINASE

The effect of ascorbic acid on the monophenolase activity of tyrosinas e, using tyrosine as substrate, has been studied. Over the ranges of a scorbic acid concentration used, no direct effect on the enzyme is fou nd. However, a shortening of the characteristic induction period of th e hydroxylation reaction is observed. The evolution of the reaction is dependent on the concentration of ascorbic acid. Low concentrations p ermit the system to reach the steady state when all ascorbic acid is c onsumed, whereas high concentrations do not. In the light of these res ults it is proposed that the influence of ascorbic acid on the reactio n is due to its ability to reduce the enzymically generated o-quinones . A relationship between the ascorbic acid concentration, and the indu ction period generated by it. with the diphenolase activity of tyrosin ase is established, which can be used as a basis for the determination of trace amounts of this reducing agent.