The DOPA Ephemera: A Recurrent Motif in Invertebrates.

3,4-Dihydroxyphenylalanine (DOPA) occurs transiently in nature as a free or peptide-bound amino acid. It is probably universally distributed in tissues and fluids of invertebrates. DOPA is a highly versatile metabolite, participating in neuroendocrine, immune, and reproductive functions, as well as in the formation of such products as bioadhesives, silks, integuments, and pigments. The mechanism by which DOPA is formed from tyrosine or peptidyl tyrosine remains to be determined in most cases. Future advances in DOPA chemistry may lead to a better understanding of the resonance between structural and sensory functions in animals.