Threonine decomposition

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. 

Decomposition of the copper complex with HjS in acid leads to allothreonine and (in about 2-fold excess) threonine. Following the pioneering work of Akabori et this reaction has been extended to a variety of metals and aldehydes and to complexes such as A- and A-Co(en)2gly with intriguing stereoselectivity behavior (optically-active allothreonine and threonine products). ... 

A group at the Academy of Sciences in Moscow 197) has synthesized chiral threonine. Derivatives of cyclic imino acids form copper complexes with glacine and carbonyl compounds. Hydroxyethylation with acetaldehyde and decomposition of the resulting complexes produced threonine with an optical purity of up to 97-100% and with threo/allo ratios of up to 19 1 197). The chiral reagents could be recovered and re-used without loss of stereoselectivity. The mechanism of this asymmetric synthesis of amino acids via glacine Schiff base/metal complexes was also discussed 197). 

Stainless steel transfer lines leading from the effluent and of the column to the detector should not be used because they will promote derivative decomposition. Glass columns should be used instead. Tyrosine, serine, and threonine are easily decomposed on hot metal surfaces. 

Not only can the a-methylene carbanion be produced and stabilized, but it can also undergo base-catalyzed aldol-type reactions without decomposition of the chelate ring. The most-studied reactions involve carbanion additions to acetaldehyde to produce threonine and allothreonine. This can be achieved for bis(glycinato)copper(II),48,49 tris(glycinato)cobalt(III)50,51 or glycinato-bis(l,2-diaminoethane)cobalt(III),52 with the best yield being obtained in the last case, where the... 

L-Threonine occurs as a white, crystalline powder. It is freely soluble in water, and insoluble in alcohol, in ether, and in chloroform. It melts with decomposition at about 256°. 

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-... 

Properties Colorless crystals, ((//-threonine) Mp 228-229C with decomposition (/(-)-threonine) (naturally occurring) mp 255-257C with decomposition ((/Z-allo-threonine), mp 250-252C. Soluble in water. Optically active. 

Table 4 shows mean values for the relative distribution of amino acids in acid hydrolyzates of humic acids and fulvic acids extracted from the same soils. These data are expressed as a-amino nitrogen of each amino acid x 100/total amino acid nitrogen. An inspection of the data in Table 4 indicates, with few minor exceptions, similarities in the amino acid composition of humic acids and fulvic acids. Acid hydrolysis appears to destroy about one-half of the amino sugars and there are losses of threonine and serine (Sowden, 1959, 1969). No corrections are made for their decomposition because the ammonia-nitrogen would then require correction, and a valid correction for it is not possible. The ammonia nitrogen increases with length of time of hydrolysis (Khan and Sowden, 1971). 

Two mechanisms have been suggested for pyrazine formation dnring smoking pyrolytic decomposition of leaf con-stitnents and nonenzymatic sugar-amine reactions. Kato et al. (2048) showed that direct pyrolysis of serine yielded pyrazine, methylpyrazine, ethylpyrazine, 2-ethyl-6-methylpyrazine, 2,6-diethylpyrazine, and 2,6-diethyl-6-methylpyrazine. Pyrolysis of threonine gave 2,5-dimethylpyrazine, trimethylpyrazine. 

The generally accepted route of formation of LAL is through the formation of dehydroalanine from cysteine, cystine, serine or phosphoserine through e-elimination reaction followed by Michael addition between the dehydroalanine and the e-amino group of lysine. The formation of LAL from the oxidized derivatives of cystine has been reported by Finley et al. (13). It was suggested that oxidation of cystine to cystine monoxide may accelerate dehydroalanine formation and subsequent LAL formation. It was also observed that very little LAL was formed through the 6-elimination of cysteine. Mel let (14) proposed that the elimination reaction in serine residues was responsible for the formation of dehydroalanine in peptides. Whitaker and Feeney (15) have reviewed the alkaline decomposition of phosphoserine and glycosylated serine or threonine residues in proteins. 

A second complicating factor is hydrolytic decomposition of certain amino acids. The most commonly used medium for keratin fiber hydrolysis is 5 to 6 A hydrochloric acid. In studies involving acid hydrolysis of keratins, partial decomposition has been reported for cystine, threonine, tyrosine [9],phenylalanine, and arginine [10] with virtually complete destruction of tryptophan [11]. 

Both serine and threonine are slowly decomposed by the action of hot strong acid. About 10% decomposition of serine and 5% decomposition of threonine occurs on refluxing in 20% HCl for 24 h (Rees, 1946). Probably the first step in the degradation is elimination of water to give 2-aminopropenoic acid or 2-aminobut-2-enoic acid, respectively (compare Section III,D). Further degradation can occur and a-aminobutyric acid has been identified as a... 

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