Metabolism of Monoamines in Invertebrates: The Relative Importance of Monoamine Oxidase in Different Phyla

A review of the occurrence of monoamine oxidase activity in invertebrates is presented. In contrast to vertebrates, invertebrates use a variety of enzymatic routes to metabolise monoamines. These routes include N-acetylation, γ-glutamyl conjugation, sugar conjugation, sulphation, β-alanyl conjugation as well as oxidative deamination. Some of these enzymatic routes appear to be strictly catabolic whereas others result in metabolites used for structural and pigmentation purposes. The development of the various catabolic routes for monoamines in different groups of invertebrates may be dependent on the physical requirements of the diverse excretory organs used by these animals.