Location and catalytic characteristics of a multipotent bacterial polyphenol oxidase

The melanogenic marine bacterium Marinomonas mediterranea contains a multip otent polyphenol oxidase (PPO) able to oxidize substrates characteristic fo r tyrosinase and laccase, Thus, this enzyme shows tyrosine hydroxylase acti vity and it catalyzes the oxidation of a wide variety of o-diphenol as well as o-methoxy-activated phenols. The study of its sensitivity to different inhibitors also revealed intermediate features between laccase and tyrosina se. It is similar to tyrosinases in its sensitivity to tropolone, but it re sembles laccases in its resistance to cinnamic acid and phenylthiourea, and in its sensitivity to fluoride anion, This enzyme is mostly membrane-bound and can be solubilized either by non-ionic detergent or lipase treatments of the membrane. The expression of this enzymatic activity is growth-phase regulated, reaching a maximum in the stationary phase of bacterial growth, but L-tyrosine, Cu(II) ions, or 2,5-xylidine do not induce it. This enzyme can be separated from a second PPO form by gel permeation chromatography. T he second PPO is located in the soluble fraction and shows a sodium dodecyl sulfate (SDS)-activated action on the characteristic substrates for tyrosi nase, L-tyrosine, and L-dopa, but it does not show activity towards laccase -specific substrates, The involvement of the multipotent PPO in melanogenes is and its relationship with the SDS-activated form and with the alternativ e functions proposed for multicopper oxidases in other microorganisms are d iscussed.