Tyrosinase action on monophenols: evidence for direct enzymatic release of o-diphenol

No oxygen isotope exchange between water and APS–sulfate at surface temperature: Evidence from quantum chemical modeling and triple-oxygen isotope experiments

“…Activation energies of corresponding reactions are calculated directly and used as theoretical determinants for the possibility of corresponding exchange channels. Hydrolysis of sulfate and phosphate esters also play a central role in a variety of biochemical processes and modeling such systems is feasible (Rodiguez-Lopez et al, 2001;Akola and Jones, 2003;Wolfenden and Yuan, 2007, and references cited therein). Independently, we examine our model results on the potential for APS-sulfate-water oxygen exchange using in vitro experiments that utilize triple-oxygen-isotope labeled solutions.…”

A Role for Tyrosinase-Related Protein 1 in 4-tert-Butylphenol-Induced Toxicity in Melanocytes

“…2,10 Tyrosinase mediates the conversion of both 4-TBP and 4-tert-catechol to quinones that react with glutathione or cysteine. 11,12 Thus, 4-TBP, a competitive inhibitor of tyrosinase, 13 is metabolized in melanocytes and may generate reactive oxygen species capable of damaging these cells and inducing apoptosis. Ironically, expression levels of tyrosinase do not correlate with sensitivity to 4-TBP-induced apoptosis, 14 suggesting an alternative enzymatic mediator may be more critical.…”

Production of o-diphenols by immobilized mushroom tyrosinase

“…However when E m binds to a monophenol (M), an inactive E m M complex is formed. The deoxy-tyrosinase form, E d , is able to bind reversibly with molecular oxygen, producing the oxy-form, E ox , which can act on both monophenols and o-diphenols, in the first case to form o-diphenols and o-quinones and in the second case o-quinones (Gómez-Fenoll et al, 2004a;Octavio de Faria et al, 2007;Rodríguez-López et al, 2001). Therefore, for monophenolase activity, it is essential that the E m form pass to E ox (E ox is the only form that can catalyze the hydroxylation of monophenols) (Gómez-Fenoll et al, 2004b;Kahn et al, 1999;Kahn and Andrawis, 1986;Rodríguez-López et al, 2001;Yamazaki and Itoh, 2003).…”

“…The deoxy-tyrosinase form, E d , is able to bind reversibly with molecular oxygen, producing the oxy-form, E ox , which can act on both monophenols and o-diphenols, in the first case to form o-diphenols and o-quinones and in the second case o-quinones (Gómez-Fenoll et al, 2004a;Octavio de Faria et al, 2007;Rodríguez-López et al, 2001). Therefore, for monophenolase activity, it is essential that the E m form pass to E ox (E ox is the only form that can catalyze the hydroxylation of monophenols) (Gómez-Fenoll et al, 2004b;Kahn et al, 1999;Kahn and Andrawis, 1986;Rodríguez-López et al, 2001;Yamazaki and Itoh, 2003). This occurs when a small quantity of o-diphenol is accumulated in the medium, which permits the above mentioned transformations, while the time taken for this concentration to be accumulated corresponds to the initial lag period observed in the monophenolase activity of tyrosinase before the steady state is reached (Rodríguez-López et al, 2001).…”

“…Therefore, for monophenolase activity, it is essential that the E m form pass to E ox (E ox is the only form that can catalyze the hydroxylation of monophenols) (Gómez-Fenoll et al, 2004b;Kahn et al, 1999;Kahn and Andrawis, 1986;Rodríguez-López et al, 2001;Yamazaki and Itoh, 2003). This occurs when a small quantity of o-diphenol is accumulated in the medium, which permits the above mentioned transformations, while the time taken for this concentration to be accumulated corresponds to the initial lag period observed in the monophenolase activity of tyrosinase before the steady state is reached (Rodríguez-López et al, 2001). When tyrosinase acts on a monophenol, the o-diphenol is obtained.…”