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The biogenesis of tropic acid in Datura stramonium Hamon, Neil Wayne


There have been two pathways postulated for the biogenesis of tropic acid in Datura stramonium. The first of these, involving the amino acid tryptophan, was proposed by Goodeve and Ramstad¹³. The second utilizes another amino acid, in this case phenylalanine, and was put forward by Leete¹⁵ and independently by Underhill and Youngken Jr.¹⁶. Since there have been these two mechanisms postulated for the biogenesis of tropic acid in this plant, one must conclude that either the two amino acids act via a common pathway or that there are in fact two separate mechanisms for tropic acid biogenesis. The purpose of this investigation was to distinguish between these two possibilities. Tryptophan-3-C¹⁴, tryptophan-(2-indolyl)-C¹⁴, indoleacetic acid-2-C¹⁴, phenylalanine-3-C¹⁴, and uniformly ring labelled phenylalanine-C¹⁴, were fed to separate, one week old, sterile, root tissue cultures of Datura stramonium. The time allowed for the metabolism of the radio-active precursor varied from three to twenty-one days. The tissue was then extracted with ethanol and this extract subjected to two-dimensional paper chromatography. Autoradiography was employed to determine the location of labelled metabolites. These metabolites were then identified by direct comparison to authentic samples chromatographed in an identical fashion. The results of this investigation show that all of the labelled precursors do give rise to labelled tropic acid. The pathway from phenylalanine appears to be the predominate mechanism for tropic acid formation in isolated Datura stramonium root tissue. The pathway from tryptophan, although apparently playing a minor role in tropic acid biosynthesis in this tissue, was shown to be a unique and independent system for the biogenesis of this aromatic acid. It is concluded therefore that there are two separate mechanisms involved in the biogenesis of tropic acid in Datura stramonium root tissue.

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