The recent discovery of an extracellular enzyme from Phanerochaete chrysospor~um capable of degrading lignin model compounds has countered the view that reactive diffusible oxygen species are responsible for lignin biodegradation. In this paper we propose a mechanism which accounts for both the results obtained in enzymatic lignin degradation studies and in studies involving active oxygen species. The quintessence of the mechanism is initial one-electron oxidation of the lignin model compounds or of a specific lignin subunit followed by subsequent breakdown reactions via radical cation intermediates. The implication of this type of mechanism on the oxidative biodegradation of the natural lignin polymer is discussed. Lignin degradation Phanerochaete chrysosporiumPeroxidase compound I Single-electron transfer Active oxygenRadical cation

The lignin-degrading, 'H,O,-dependent oxygenase' from Phanerochaete chrysosporium oxidised veratryl alcohol without incorporating oxygen into the substrate. It also catalysed a-8 cleavage of a non-phenolic diarylpropane substrate in the absence of oxygen. Studies with tris(phenanthroline)iron (III) established the importance of single-electron transfer in bringing about a-/3 cleavage. We propose that the lignin-degrading enzyme functions not as an oxygenase but as a peroxidase and that the oxidation reactions are brought about by initial single-electron transfer between the aromatic ring and a high redox oxy-ferry1 active site in the enzyme.

BackgroundNeonatal nurse practitioners are often the front line providers in discussing unexpected news with parents. This study seeks to evaluate whether a simulation based Difficult Conversations Workshop for neonatal nurse practitioners leads to improved skills in conducting difficult conversations.

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