The copper-containing oxidases tyrosinase and laccase have been intensively investigated for decades. For a long time, research into eukaryotic tyrosinases was hampered by low purification yields, but significant progress was recently made with those from soil microorganisms. New insights were obtained, especially in relation to structural and catalytic data. The formation of protective melanins is one well-established task of tyrosinases in eukaryotes. The physiological importance of the extracellular tyrosinases produced by the bacterium Streptomyces is not well understood. Tyrosine is neither an inducer of enzyme production nor a probable substrate in soil.

More assured information exists on the structural and biochemical properties of laccases from fungal sources. Many studies demonstrate their physiological role in the detoxification of phenolic compounds. Their occurrence in soils underlines their ecological importance in the metabolic turnover of complex organic polymers such as lignin and humic matter. In ectomycorrhizal symbiotic fungi, they contribute to the nutrition of trees by mobilizing and transporting nutrients to the plant roots. The specific monohydroxylase activities of tyrosinases and the high nonspecific oxidation capacities of laccases can be exploited for numerous biotechnological processes. The screening of natural sources and genetic engineering will further expand our knowledge and applications of these old-fashioned metalloenzymes.

Acknowledgements The author dedicates this contribution to Prof. Hans-J├╝rgen Kutzner on the occasion of his eightieth birthday. Many thanks to Lo Gorton (Lund, Sweden) and Sergey Shleev (Moscow, Russia) for their kind permission to use some of their graphical materials in this chapter.

Organic Gardeners Composting

Organic Gardeners Composting

Have you always wanted to grow your own vegetables but didn't know what to do? Here are the best tips on how to become a true and envied organic gardner.

Get My Free Ebook

Post a comment