Assessing the catalytic activity of three different sources of tyrosinase: A study of the oxidation of mono- and difluorinated monophenols

Tyrosinase (tyr) purified from Pseudomonas putida F6, Streptomyces antibioticus, and Agaricus bisporus (mushroom) oxidises 3 regioisomers of fluorophenol as well as 3,4-difluorophenol (3,4FP). The catalytic efficiency (kcat/Km) of tyrosinase towards any one substrate is different for each enzyme source. Oftentimes a large difference in affinity (Km), and turnover (kcat) is observed for different enzyme sources with the same substrate. The best catalytic efficiency towards a fluorinated substrate was observed for P. putida F6 tyr with 4-fluorophenol (4FP). The presence of a second fluorine on the aromatic ring (3,4FP) resulted in a decrease in the catalytic efficiency of all three enzymes compared to values for 4FP. However, the Km value for 3,4FP decreased for P. putida F6 tyr indicating a higher affinity for P. putida F6 tyr for 3,4FP compared to 4FP. Furthermore the kcat value for 3,4FP increased for mushroom tyr in comparison to the value for 4FP indicating a higher maximum turnover of 3,4FP compared to 4FP for mushroom tyr. All three sources of tyr exhibited lower catalytic efficiencies for 3-fluorophenol (3FP) and 2-fluorophenol (2FP) compared to 4FP. However, the Km value for 2FP was lower than that for 3FP for both S. antibioticus and mushroom tyr indicating a higher affinity for 2FP over 3FP.