Activation of a latent mushroom (Agaricus bisporus) tyrosinase isoform by sodium dodecyl sulfate (SDS). kinetic properties of the SDS-activated isoform

This study reports the activation of a latent mushroom tyrosinase isoform b y sodium dodecyl sulfate (SDS). The activation process of latent mushroom t yrosinase by SDS is characterized by the presence of a Tag period (tau) pri or to the attainment of a steady-state rate (V-ss). This could be related t o a slow conformational change of the latent enzyme to render the active is oform. The molecular size of the latent isoform was 67 kDa as determined by SDS-PAGE and western-blotting assays. This size did not change after activ ation by SDS. The molecular size of the protease-activated isoform was 43 k Da. tau and V-ss displayed a sigmoidal relationship to the concentration of SDS, but tau was not dependent on o-diphenol or enzyme concentration. Incr easing SDS concentrations decreased tau, but then lower V-ss values were de tected because of a possible excess of unfolding and subsequent denaturatio n of the protein. The same reaction mechanism operated in both SDS-activate d and protease-activated tyrosinase isoforms despite their different kineti c features. A possible mechanism for the activation of this latent tyrosina se by SDS is proposed.