Kinetic and paramagnetic NMR investigations of the inhibition of Streptomyces antibioticus tyrosinase

A scaled-up isolation and purification procedure is described for tyrosinas e from Streptomyces antibioticus. Kinetic studies of the enzyme catalysed c onversion of L-3,4-dihydroxyphenylalanine (L-DOPA) into DOPAchrome show tha t kojic acid, L-mimosine, p-toluic acid and benzoic acid exhibit competitiv e inhibition with inhibition constants of 3.4, 30, 1.9 X 10(2) and 8.0 X 10 (2) mu M, respectively. Paramagnetic NMR techniques appear well suited to s tudy the binding of inhibitors to the active site. From the variation of th e NMR shifts with temperature a value of -2J = 156 +/- 6 cm(-1) is derived for the exchange coupling between the unpaired spins on the two Cu(II) ions in the active site of the met-tyrosinase/kojic acid complex. (C) 2000 Else vier Science B.V. All rights reserved.