Amino acids threonine

Molecules like lactic acid, alanine, and glyceraldehyde are relatively simple because each has only one chirality center and only two stereoisomers. The situation becomes more complex, however, with molecules that have more than one chirality center. As a general rule, a molecule with n chirality centers can have up to 2n stereoisomers (although it may have fewer, as we ll see shortly). Take the amino acid threonine (2-amino-3-hydroxybutanoic acid), for example. Since threonine has two chirality centers (C2 and C3), there are four possible stereoisomers, as shown in Figure 9.10. Check for yourself that the R,S configurations are correct. 

Problem 26.3 The amino acid threonine, (2S,3ft)-2-amino-3-hydroxybutanoic acid, has two chirality centers. 

Protein content of dehulled Trapper field peas is negatively correlated with the amino acids threonine, cystine, glycine, alanine, methionine, and lysine and positively correlated with glutamic acid and arginine (8). Holt and Sosulski (19) obtained similar correlations with Century field peas for all amino acids except glutamic acid. Other investigators (20) also found that sulfur amino acids (cys, met) are negatively correlated with protein content. 

Two of the protein amino acids, threonine and isoleucine, have two chiral centres therefore, diaste-reoisomeric forms are possible. In proteins, each of these amino acids exists in a single diastereoisomeric form. 

Vitamins and Health Supplements Guide (2005). http //www.vitamins-supplements.org/ amino-acids/threonine.php Threonine. 

Stereoselective formation of 3-alkyl-6-methoxy-2,5-piperazine-dione derivatives by the addition of methanol in the presence of NBS to 3-alkyl-6-alkylidene-2,5-piperazinediones was recently reported by Shin et al. 232 The asymmetric induction in this reaction was accomplished by the chiral center of a derivative of the natural proteinogenic chiral amino acid threonine. 

Kirchgessner and Steinhart (52) studied the in vitro digestion of soy protein isolate with pepsin. They showed that a relatively higher percentage of the essential amino acids threonine, valine, isoleucine, leucine and phenylalanine were found in the undigested residue and therefore would be present in lower proportions in the hydrolysate. Myers et al. ( ) hydrolyzed a soy protein isolate with a fungal acid protease. They also found that the essential amino acid content of the hydrolyzate was lower than the isolate, but, as prepared by their continuous process, the hydrolyzate PER was not significantly reduced as compared to the isolate PER. 

For instance, if such a substitution is induced in the tobacco mosaic virus genome, changes in the viral protein can be detected, which correlate with the mutation. This has been made possible because the viral protein has been characterized. Thus, it is found that the amino acid threonine is replaced by isoleucine. It is also clear that several triplet codes in the nucleic acid specify the amino acid threonine, namely AC A, AGG, ACC, and ACU, emphasizing the degeneracy of the code. 

We have seen examples of molecules with one chiral center that exist in two mirror-image configurations, which we call enantiomers. What happens when there is more than one chiral center How many stereoisomers should we expect Consider the stereoisomers of the important amino acid, threonine, (2-amino-3-hydroxybutanoic acid). For this substance, if we write all of the possible configurations of its two chiral carbons, we have four different projection formulas, 19-22, corresponding to four different stereoisomers ... 

Despite the apparent advantages in the amide-containing amino acids, we do not always find amides used as part of the recognition sequence. For example, the trp repressor does not use any amides. The basic amino acids, lysine and arginine, and the hydroxylic amino acid, threonine, are the main interacting amino acids in the trp repressor. The side... 

The monophosphines gave optical yields of 2.1 and 0.5% respectively, but with DIOP a best result of 23% was obtained.371 The product of this hydroformylation is a potential precursor for the amino acid threonine. 

Figure 1. Shortened chromatogram of amino acids in air-dried carrots. Peak C represents Amadori compounds formed by reaction between glucose and the amino acids threonine, serine, asparagine, glutamic acid, and glutamine.

Look at the amino acid threonine (S-amino-U-hydroiqdmtanoic acid >, lor I example. Since direonine has two chinalfty centers [Pg.340]

Problem 26.5 The amino acid threonine. (2> f,3i )-2-amino 3-hydrosybuUmoic netd, hau two diiraf-ily centjem. Draw a PiecKer projection of threonine. 

Problem 36.8 Draw all possible stereoisomeric formulas for the amino acid threonine. Naturally occurring threonine gets its name from its relationship to the letrose threose on this basis which is the correct configuration for natural threonine ... 

The laboratory of Sidransky et al.52-53 62 in 1967-1968 demonstrated that L-tryptophan alone elicited a response of hepatic polyribosomes toward heavier aggregation as well as an enhancement of protein synthesis as measured in vivo or in vitro. The single administration of tryptophan alone, but not of one of three other essential amino acids (threonine, methionine, or isoleucine), elicited a stimulatory hepatic response that was similar to that obtained with a complete amino acid mixture.53 Earlier, Feigelson et al.63 in 1959 had reported that the parenteral administration of tryptophan in the rat produced a transient elevation in hepatic protein synthesis as determined by measuring 2[14C]glycine incorporation into hepatic protein. Subsequent studies from other laboratories60 64-69 confirmed the stimulatory effect of tryptophan on hepatic protein synthesis. 

This posttranscriptional modification occurs in more than 30% of proteins in mammals. This involves the addition of one or more PO4 groups to particular amino acids in a protein. In mammalian cells, PO4 groups are added to the amino acids threonine, serine, or tyrosine of the protein. In contrast, amino acids such as aspartic, glutamic, and histidine are phosphorylated in prokaryotes, instead of tyrosine, serine, and threonine in eukaryotes. Occasionally in both prokaryotes and eukaryotes, phosphorylation occurs in arginine, lysine, and cystein residues of the protein. The ratio of phosphorylation of the three amino acid residues in mammalian cells is 1000 100 1 for threonine, serine, and tyrosine. Proteins are phosphorylated at more than one site, and usually a mixture of phosphorylated isomers with different levels of phosphorylation exists in the cell. Phosphorylation adds a negative charge to the proteins with the addition of the PC>4 group. 

Sorghum protein also appears to have low levels of the indispensable amino acids threonine and tr) tophan and high levels of leucine (reviewed by Klopfenstein and Hoseney, 1995). However, as shown in Table 2.4, contrary to earlier suggestions (Klopfenstein and Hoseney,... 

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