5-Methoxy- and 5-Hydroxyindoles in the skin of <i>Bufo alvarius</i>

Abstract

The skin of <i>Bufo alvarius</i>, a desert toad of Arizona, contains a number of indolealkylamines and their metabolites belonging to the common series of 5-hydroxyindolealkylamines and to the unusual series of 5-methoxyindolealkyIamines. The most abundant representative of 5-hydroxyindolealkylamines is, as in numerous other toads, bufotenine (up to 3 mg per g dry skin), the most abundant representative of 5-methoxyindolealkylamines, O-methylbufotenine. In parotoid and coxal glands as much as 5–15 per cent of the dry weight is made up by this compound. Natural O-methylbufotenine has been isolated in a pure form and its identity with synthetic O-methylbufotenine definitely established. The <i>B. alvarius</i> skin presents three sulphur-containing indolealkylamines: one is bufoviridine, the well known O-sulphate of bufotenine, the other two are completely new compounds with sulphuric acid probably attached to the > NH group of the indole nucleus. All the hitherto described metabolites arising from the oxidative deamination of 5-hydroxy- and 5-methoxy-indolealkylamines may be found in the <i>B. alvarius</i> skin: 5-hydroxytryptophol, 5-hydroxyindoleacetic acid, 5-methoxytryptophol and 5-methoxyindoleacetic acid. The occurrence of the above compounds points to the necessary presence in <i>B. alvarius</i> skin of a number of enzymes: tryptophan 5-hydroxylase, catalysing the formation of 5-hydroxytryptophan, aromatic L-aminoacid decarboxylase producing the decarboxylation of 5-hydroxytryptophan to 5-hydroxytryptamine, N-methyl transferase and 5-hydroxyindole-O-methyl transferase giving origin to the N-methyl and O-methylindolealkylamines, and finally sulphoconjugases catalysing the linkage of sulphuric acid to the 5-hydroxy group and the > NH group of the indole nucleus. The exceptionally rich sample card of indolealkylamines in the skin of <i>B. alvarius</i> seems of interest not only from the point of view of comparative biochemistry, but also from that of comparative enzymology and biochemical taxonomy.