Tryptophan decomposition

C, soluble in water and alcohol. It occurs in woad as the glucoside indican, and in mammalian urine, combined with sulphuric acid, as an ester, also called indican. It arises in the body from the bacterial decomposition of tryptophan. 

The deterruination of amino acids in proteins requires pretreatment by either acid or alkaline hydrolysis. However, L-tryptophan is decomposed by acid, and the racemi2ation of several amino acids takes place during alkaline hydrolysis. Moreover, it is very difficult to confirm the presence of cysteine in either case. The use of methanesulfonic acid (18) and mercaptoethanesulfonic acid (19) as the protein hydroly2ing reagent to prevent decomposition of L-tryptophan and L-cysteine is recommended. En2ymatic hydrolysis of proteins has been studied (20). 

Protein Hydrolysis. Acid hydrolysis of protein by 6 MHQ in a sealed tube is generally used (110°C, 24-h). During hydrolysis, slight decomposition takes place in serine (ca 10%) and threonine (ca 5%). Cystine and tryptophan in protein cannot be deterruined by this method because of complete decomposition. 

Tyrosine, tryptophan and tetracyline are filter-sterilised to prevent decomposition by heat sterilisation. 

The occurrence of alanine in proteins was first shown by Schutzen-berger, who did not actually identify his product with the synthetical one Weyl in l88i obtained it as a decomposition product of silk and showed that his preparation was similar in properties to Strecker s synthetical alanine. He thus established it as a constituent of a protein molecule. The researches of Emil P ischer have shown that alanine is a constant constituent of all proteins. It is worthy of note that of the eighteen definitely determined units of a protein molecule, six of them, namely, isoleucine, phenylalanine, tyrosine, serine, histidine and tryptophane, are derivatives of a-aminopropionic acid. 

Cobaltn-Schiff base complexes, e.g. Co(salen),567 Co(acacen)568 and cobalt(II) porphyrins,569 e.g. Co(TPP), are effective catalysts for the selective oxygenation of 3-substituted indoles to keto amides (equation 249), a reaction which can be considered as a model for the heme-containing enzyme tryptophan-2,3-dioxygenase (equation 21).66 This reaction has been shown to proceed via a ternary complex, Co-02-indole, with probable structure (175), which is converted into indolenyl hydroperoxide (176). Decomposition of (176) to the keto amide (174) readily occurs in the presence of Co(TPP), presumably via formation of a dioxetane intermediate (177).569,56 Catalytic oxygenolysis of flavonols readily occurs in the presence of Co(salen) and involves a loss of one mole of CO (equation 251).570... 

Imine formation, the Amadori rearrangement, and aminoketose decomposition, with glucose or xylose and tryptophan, led to activation volumes of 14, + 8, and +17 ml, mol pressure thus accelerating the first, but retarding the other two reactions.106 As a consequence, the formation of certain volatiles, such as norfuraneol at pH 7 and 2-methylpyrazine at pH 10 in lysine-xylose systems, is greatly decreased.107... 

Some of these compounds have been detected upon thermal decomposition of certain foods, amino acids, and proteins. Significant amounts of compound (13), known as norharman, and its 9-methyl derivative, commonly called harman, have been found in tryptophan pyrolyzates. Similarly, cigarette smoke condensate has been found to contain significant amounts of both of these compounds <82JC331>. 

The yellowing of silk in sunlight has been related to the discoloration of tryptophan formed by oxidative decomposition of silk fibroin... 

Such chemical changes may lead to compounds that are not hydrolyzable by intestinal enzymes or to modifications of the peptide side chains that render certain amino acids unavailable. Mild heat treatments in the presence of water can significantly improve the protein s nutritional value in some cases. Sulfur-containing amino acids may become more available and certain antinutritional factors such as the trypsin inhibitors of soybeans may be deactivated. Excessive heat in the absence of water can be detrimental to protein quality for example, in fish proteins, tryptophan, arginine, methionine, and lysine may be damaged. A number of chemical reactions may take place during heat treatment including decomposition, dehydration of serine and threonine, loss of sulfur from cysteine, oxidation of cysteine and methio-... 

The decomposition of hypaphorine into indole and trimethylamine occurs slowly in the rotting wood of Abrus precatorius L., and is responsible for its fecal odor. It also led van Romburgh (30) to propose the correct structure for hypaphorine, which was soon established by synthesis from L-tryptophan (17). 

Pseudoakuammicine is the first racemic base to be discovered in the strychnine-yohimbine series of alkaloids, and the question of its origin naturally arises. The only stage in the extraction of Picralima seeds during which racemization of akuammicine might have occurred involved prolonged percolation with hot methanol however, as already discussed, akuammicine is not racemized under these conditions but suffers a more extensive decomposition. In any event, such a racemization would necessarily involve fission of the 3,7 and 15,16 bonds, followed by a nonspecific resynthesis, which is considered to be a very unlikely possibility. It was therefore suggested that, in the plant, pseudoakuammicine is produced by a nonspecific biosynthesis this would accord with its formation from a tryptophan-phenylalanine precursor, but not from an optically pure prephenic acid derivative (40). 

Tr3Tptophane.—As an intermediate product in the decomposition of proteins we have the amino acid known as tryptophane which may be obtained by the acid hydrolysis of most proteins (p. 389). Tryptophane may be considered either as an indole or skatole derivative. 

On further decomposition tryptophane yields either indole or skatole. Not only are these final protein decomposition products present in the faeces, but they become absorbed from the intestine and pass into the urine where they are present as normal constituents, having first undergone oxidation forming indoxyl and skatoxyl which then esterify with sulphuric acid yielding, in the case of indole, indoxyl sulphuric acid, the potassium salt of which has been wrongly termed indican. 

Formyltryptophan is stable up to pH 7 at room temperature. The decomposition of the derivative back to tryptophan at alkaline pH forms the basis of the deformylation procedure. The protein derivative (approx. 5 mg/ml) is dissolved in 0.05 M NH4OH-NH4CI, pH 9.5, containing 6 M guanidine hydrochloride. After incubation at room temperature for 16 hr, the protein is dialyzed and lyophilized. 

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