Biochemistry of Amino Acids - A. Majster 1961

Intermediary Metabolism of Amino Acids
Tryptophan
Other Tryptophan Metabolites

In A number of Bacteria, The breakdown of tryptophan occurs via the tryptophanase reaction, yielding indole, pyruvic acid, and ammonia:

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First discovered by Hopkins and Cole [862], this reaction was subsequently investigated in detail by other researchers [863, 864]. Wood and co-workers [865] isolated enzyme preparations from E. coli that catalyze this conversion and demonstrated that Pyridoxal phosphate acts as its coenzyme. The reaction apparently requires the presence of potassium, ammonium, and possibly iron ions [866, 867]. Snell and associates [731] suggested that The Mechanism of this reaction involves the Cleavage of the side chain from a complex consisting of pyridoxal, tryptophan, and a metal:

During the breakdown of indole in certain bacteria, The formation of indoxyl, indican, indigo, and indirubin is observed. These compounds have been detected in normal human urine, and they are believed to be synthesized by intestinal flora bacteria [881–883].

Fig. 19. Summary scheme of tryptophan transformations.

It has been hypothesized that some bacteria can degrade indole through the following sequence of reactions [884]:

It appears that the molecules of certain Alkaloids (gramine, physostigmine, strychnine, cinchonine, emetine, etc.) are formed partially from tryptophan; extensive research has been devoted to their biogenesis [885–888]. In an interesting paper, van Tamelen [889] discusses the relationship between 5-hydroxytryptophan and lysergic acid.

Experiments utilizing ring-tritiated nicotinic acid and 14C-labeled nicotinic acid preparations have recently demonstrated that this acid serves as a precursor of nicotine in the tobacco plant [1131].



Last update: 06/08/2026

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