Tryptamine,(1-naphthyl) ethylamine and phenethylamine derivatives were tested as substrates of ovine pineal serotonin-N-acetyl transferase (5-HT-NAT), a key enzyme involved in the synthesis of melatonin. Almost all of the indole derivatives possessed affinity similar to that of tryptamine (Km= 0.05 mM), while the substituted naphthalene and phenyl derivatives were less potent. However, the Km values seem be influenced by the steric ...