Biochemistry of Amino Acids - A. Majster 1961

Intermediate Amino Acid Metabolism
Tryptophan
The role of tryptophan in plant growth hormone biosynthesis

The plant Growth Hormone (auxin) was first isolated from human urine [857, 869] and only later discovered in plants, where it was identified as indoleacetic acid. It is known that Tryptophan is required for The Biosynthesis of indoleacetic acid [868, 870–872], although The Mechanism of this transformation remains poorly understood. Tryptophan can be converted into tryptamine via decarboxylation, with the latter subsequently oxidized through the corresponding aldehyde into indoleacetic acid. Alternatively, tryptophan may be converted into indoleacetic acid via Oxidative Deamination or Transamination, followed by The oxidative decarboxylation of indolepyruvic acid. Tryptamine [873], indolepyruvic acid [874], and indoleacetaldehyde [875] have all been identified in biological samples. Plants are capable of producing auxin from both tryptamine [868, 871, 876] and indolepyruvic acid [868, 871]. Indoleacetonitrile, which exhibits potent auxin-like activity, has been found in cabbage [877]. This nitrile may be formed through The oxidation of tryptamine and subsequently converted into indoleacetic acid via Hydrolysis; however, the occurrence of such reactions has not yet been experimentally proven. The Oxidative Decarboxylation of indoleacetic acid yielding indole-3-aldehyde has been investigated by several researchers [878–880].