Partial purification and characterisation of two actinomycete tyrosinases and their application in cross-linking reactions

Abstract

Actinomycetes are a ubiquitous group of bacteria, and are hypothesised to produce tyrosinases for pro-tection against the potential toxic effect of phenolic compounds and for the production of melanin. In thisstudy, tyrosinase production by Streptomyces pharetrae CZA14T(CZA14Tyr) and Streptomyces polyantibi-oticus SPRT(SPRTyr) was optimised. The enzymes were partially purified and biochemically characterisedto determine their suitability for industrial applications. SPRTyr was stable up to 40◦C and at pH 4.5–10.0,while CZA14Tyr was stable up to 40◦C and at pH 6.5–10.0. The enzymes showed variable stability in thepresence of water-miscible organic solvents and were able to oxidize l-DOPA in the presence of these sol-vents. A limited inhibitory effect was observed with arbutin, EDTA, sodium chloride and sodium dodecylsulphate, while both enzymes were strongly inhibited by the reducing agents used in this study. Inhibi-tion of enzyme activity was observed in the presence of 1 mM Cu2+and 5 mM Co2+for SPRTyr, and 5 mMFe2+and 5 mM Zn2+for CZA14Tyr. When applied in various cross-linking reactions both tyrosinases wereable to cross-link casein and gelatine in the absence of a phenolic compound, showing potential forapplication in the food industry and for the production of biomaterials.