L-Alanine Ala

It is a peptide containing 27 amino acid residues containing the amino acids L-histidine (His) L-aspartic acid (Asp) L-serine (Ser) glycine (Gly) L-threonine (Thr) L-phenyl-alanine (Phe) L-glutamic acid (Glu) L-glutamine [Glu(NHj)] L-leucine (Leu) L-arginine (Arg) L-alanine (Ala) and L-valinamide (Va -NHj). 

Adsorption of a series of amino acids and other compounds related to L-dopa has been studied [84], including L-dopa (LD), L-tyrosine (TYR), L-cysteine (CYS), L-phenylatamine (PHE), L-alanine (ALA), dopamine (DA), catechol (CT), 3-mercaptopropionic acid (MPA), and 2-aminoethanethiol (AET). 

Abbreviations Ala, L-alanine Ala, fully N-labelled L-alanine Leu, L-leucine Leu, fully N-labelled L-leucine NHBu, n-butyl amide o-helix, right-handed a-helix /3-sheet, anti-parallel /3-sheet. 

Table 22.4 shows the values of Rn for some solid polypeptides, determined by using Equations (22.1a-e) through the observation of the amide carbonyl-carbon chemical shift as listed are solid polyglycine[(Gly) ], poly(L-alanine)[(Ala) ], poly(L-valine)[(Val) ], and poly(L-leucine)[(Leu) ] with several conformations such as righthanded a-helix (aR-helix), j8-sheet, 3i- and (UL-helix. In these homopolypeptides, the Rn o values determined for the /3-sheet form are constant in the range of 3.0-3.1 A, regardless of amino acid residue species. The Rn-.-o value for the 3i-helix in (Gly) is... 

The fundamental problem in the synthesis of peptides is that amino acids must be connected in a defined sequence by specifically forming a peptide bond between the carboxylic acid group of one amino acid and the amino group of another. The potential difficulties arising in such endeavors may be illustrated by considering the synthesis of the simple dipeptide Ala-Phe from the individual amino acids L-alanine (Ala) (3) and L-phenylalanine (Phe) (4), as seen in Equation 24.2. Formation of peptide bonds in a random manner could lead to four different dipeptides. This mixture arises because the carboxylic acid of Ala may react with either the amino... 

L-Alanine (Ala) N-Acetylmuramic acid Bacterial cell wall peptidoglycan... 

Synthetic polypeptides consist of repeating sequences of certain amino acids and their structures are not as complicated as those of proteins. Eor this reason, synthetic polypeptides are sometimes used as model compounds for proteins. Their preferred conformations are classified as a helix, P sheet, 0) helix and so on. High-resolution solid-state C NMR spectroscopy has proved to be a very powerful tool for determining the structure of polypeptides in the crystalline state. Eor example, C CP MAS NMR spectra of solid poly(L-alanine) ([Ala] J show the Ca, Cp and C=0 carbon signals to be well resolved between the a helix and P sheet forms. The chemical shifts of the Ca and C=0 carbons of the a helix are displaced sig nilicantly to high frequency by 4.2 and 4.6 ppm, re spectively, relative to those of the P sheet form, while the shift of the Cp carbon of the a heUx is displaced to low frequency by about 5 ppm with respect to that of the P sheet. Eor this reason, the value of the C shift can be used to describe the local conformation. In addition, the C shifts of randomly coiled [Ala] in trifluoroacetic acid solution have values between those of the a helix and P sheet forms. The absolute C shifts of the Ca and Cp carbons are affected by the chemical structure of the individual amino acid residues and can be used effectively for conformational studies of particular amino acid residues in polypeptides and proteins. On the other hand, the C=0 shifts do not seem to be affected by residue structure and can be used for diagnosing the main chain conformation. 

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