SOME ASPECTS OF TYROSINE SECONDARY METABOLISM

The origin and fate of some tyrosine secondary metabolites within spec ialized eukaryotic cells are discussed in the light of our knowledge o f the plasma environment to which they are exposed throughout their li fetime. Attention is focused on ar-dihydroxy and -trihydroxy derivativ es and the corresponding quinoidal counterparts, as well as on the enz ymic activities involved in the formation and degradation of these pot entially toxic molecules. Some physiopathological and pharmacological implications of the above-mentioned topics are considered, taking into account the well known toxicity of reactive intermediates in molecula r oxygen reduction, as well as the reactivity of both semiquinonic and quinonic products of catecholamine oxidation. (C) 1998 Elsevier Scien ce Inc.