Evidence for biosynthesis and catabolism of monoamines in the sea pansy Renilla koellikeri (Cnidaria).

The biosynthesis of catecholamines and indoleamines was investigated in the sea pansy Renilla koellikeri by radiochemical screening of tissue samples exposed in vivo to labelled amino acid precursors and analysed by high-performance liquid chromatography coupled with electrochemical detection. Incubation of sea pansy tissues in [3H]tyrosine resulted in substantial accumulation of radioactivity recovered in chromatograms coeluting with tyrosine and 4-hydroxy-3-methoxy mandelic acid and, to a lesser extent, with 3,4-dihydroxy-phenylalanine, dopamine, norepinephrine, epinephrine, normetanephrine and 3,4-dihydroxyphenyl acetic acid. The catecholamine synthesis inhibitor alpha-methyl-p-tyrosine effectively reduced several of these [3H]tyrosine by-products formed as well as endogenous stores of these amines. Incubations in [3H]tryptophan resulted in large amounts of radioactivity associated with liquid chromatographic peaks coeluting with tryptophan and 5-hydroxytryptophan and lesser amounts with 5-hydroxytryptamine, N-acetyl-5-hydroxytryptamine and 5-hydroxy-3-indole acetic acid. The indoleamine synthesis inhibitor p-chlorophenylalanine reduced the amounts of products formed and depleted stores of the endogenous indoleamines. Enzyme activities which appear to involve tyrosine hydroxylase (EC 1. 12. 16. 2), tryptophan hydroxylase (EC 1. 14. 16. 4) and phenylethanolamine N-methyltransferase (EC 2. 1. 1. 28) were also detected in rachidial tissues by HPLC analysis of reaction products (hydroxylases) and by a radioenzymatic assay (methyltransferase). The sea pansy being a representative of the earliest invertebrates possessing a nervous system, these results support the hypothesis that vertebrate-like enzymatic pathways for the biosynthesis and degradation of monoamine neurotransmitters were conserved throughout evolution.