Other amino acids

The colour test is not specific for a-amino acids other primary amino compounds and also ammonia give a blue colouration with ninhydrin. 

Chymotrypsin shows a strong preference for hydrolyzing peptide bonds formed by the carboxyl groups of the aromatic amino acids, phenylalanine, tyrosine, and tryptophan. Flowever, over time chymotrypsin also hydrolyzes amide bonds involving amino acids other than Phe, Tyr, or Trp. Peptide bonds having leucine-donated carboxyls become particularly susceptible. Thus, the specificity... 

The enolic form of 2 was confirmed by a ferric chloride color reaction and by its acidity and ultraviolet spectrum, A-Aroyl derivatives of amino acids other than glycine fail to form such azlactones, probably because the stabilization afforded by enolization cannot occur. 

This field has also inspired the development of a range of pseudo-peptides, that is polyamides composed of amino acids other than a-amino acids. These include for instance peptoids, /9-amino acid oligomers and also compounds such as peptide nucleic acids and DNA binding polyamides, all of which share the amide (peptide) chemistry with natural peptides. 

Aminotransferase (transaminase) reactions form pymvate from alanine, oxaloacetate from aspartate, and a-ketoglutarate from glutamate. Because these reactions are reversible, the cycle also serves as a source of carbon skeletons for the synthesis of these amino acids. Other amino acids contribute to gluconeogenesis because their carbon skeletons give rise to citric acid cycle... 

Twenty different amino acids are used to build proteins in living cells. The simplest is glycine, where R = H. In each of the 19 amino acids other than glycine, the side chain begins with a carbon atom. The side chains in naturally occurring amino acids are shown in Figure 13-32. 

Distortion of the plasma aminogram in individuals with an aminoaciduria also may lead to a relative failure of brain protein synthesis. Thus, in mice with a deficiency of phenylalanine hydroxylase, the blood concentration of phenylalanine is more than 20 times greater than the control value, leading to partial saturation of the transport system and a diminution in the brain level of neutral amino acids other than phenylalanine. Rates of protein synthesis were concomitantly reduced [8]. 

Activated esters (see Section 2.9) with 1-hydroxybenzotriazole as a catalyst are employed — pentafluorophenyl or 4-oxo-3,4-dihydrobenzotriazin-3-yl esters in particular for continuous-flow systems and special cases such as dicarboxylic amino acids. Other activated esters are not reactive enough. An alternative is preparation of benzotriazolyl esters using a carbodiimide followed by addition of the solution to the peptide-resin. 

Based on our current understanding of ribosomal protein synthesis, several strategies have been developed to incorporate amino acids other than the 20 standard proteinogenic amino acids into a peptide using the ribosomal machinery . This allows for the design of peptides with novel properties. On the one hand, such a system can be used to synthesize nonstandard peptides that are important pharmaceuticals. In nature, such peptides are produced by nonribosomal peptide synthetases, which operate in complex pathways. On the other hand, non-natural residues are a useful tool in biochemistry and biophysics to study proteins. For example, incorporation of non-natural residues by the ribosome allows for site-specific labeling of proteins with spin labels for electron paramagnetic resonance spectroscopy, with... 

Not only moulds, but also yeasts can be employed in the separation of optically active compounds as was shown by F. Ehrlich in 1906, who obtained in this way 1-alanine, d-leucine, 1-valine. Further, amino acids, other than those which occur in nature, can be separated by moulds and yeasts into their components, eg., n-aminocaproic acid, methylethyl-aminoacetic acid. 

The effect of oncogenic mutations at position 61 can also be explained using the Ras-GAP complex. GIn61 has a central function in GTP hydrolysis in that it contacts and coordinates the hydrolytic water molecule and the O-atom of y-phosphate of GTP and thus stabilizes the transition state. Amino acids with other side chains apparently cannot fulfil this function, as shown by the oncogenic effect of Ghi61 mutants in which Ghi61 is replaced by other amino acids (other than Glu). 

The MEK kinases (MAPKK kinases) are Ser/Thr-specific protein kinases and are the entry point for signal transduction in a MAPK module. The best characterized representative, Raf-1 kinase, is activated by Ras protein in its GTP-bound form. Raf kinase phosphorylates downstream MEK proteins at two Ser residues, which are separated by three other amino acids. All known MEK proteins have a similar phosphorylation site in the conserved sequence LID/NSXANS/T (X any amino acid). Other representatives of the MEK kinase group are Mos kinase and the protein kinases MEKKl—3. 

This procedure was improved 123 for the synthesis of building units based on amino acids other than Gly, but with nonfunctionalized side chains (Table 6). To suppress the 3-elim-ination and racemization side reactions, triflates of a-hydroxycarboxylic acid esters 124 34 (L = OTf, Scheme 19) were used as substrates for the nucleophilic substitution. In order to prevent polyalkylation, the nucleophilic amine of to-BocNH- or co-tBu02C-alkylamines 33 were temporarily protected with the benzyl group. 115116 This protection also improved the yields and purity of Gly-based building units. In this case commercially available benzyl bromoacetate 34 (L=Br) was used as the substrate. In both cases the nucleophilic sub-... 

Molecular defects that give rise to dysfibrinogenemias are commonly caused by single base mutations that lead to the substitution of a single amino acid. Other mutations can give rise to a stop codon, resulting in a... 

An ion-pair derived from the substrate and solid NaOH forms a cation-assisted dimeric hydrophobic complex with catalyst 39c, and the deprotonated substrate occupies the apical coordination site of one of the Cu(II) ions of the complexes. Alkylation proceeds preferentially on the re-face of the enolate to produce amino acid derivatives with high enantioselectivity. However, amino ester enolates derived from amino acids other than glycine and alanine with R1 side chains are likely to hinder the re-face of enolate, resulting in a diminishing reaction rate and enantioselectivity (Table 7.5). The salen-Cu(II) complex helps to transfer the ion-pair in organic solvents, and at the same time fixes the orientation of the coordinated carbanion in the transition state which, on alkylation, releases the catalyst to continue the cycle. 

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