Protein-derived amino acids

FIGURE 4.5 The structures of some ammo acids that are not normally found in proteins but that perform other important biological functions. Epinephrine, histamine, and serotonin, although not amino acids, are derived from and closely related to amino acids. 

Animals, including humans, cannot synthesise all the different amino adds they need and thus require them in their diet. These amino adds are called the essential amino acids. Proteins in food are hydrolysed in the digestive tract and the resulting amino acids are reassembled into proteins within the animal s cells. All animals are ultimately dependent on plants for protein, as it is plants that create protein by combining inorganic nitrogen from the soil (as nitrate) with organic molecules derived from carbon from the atmosphere (as CO2). 

Most cases of AzD show cerebrovascular amyloid deposits and the amyloid protein of senile plaques is the same as that found in blood vessels. It is referred to as )S-amyloid protein and is part of a 695, 751 or 770 amino-acid amyloid precursor protein APP, which is a transmembrane protein and although its precise function is not clear, it is widely distributed and APP knock-out mice show reduced motor function. Normally so-called short 40 amino-acid-soluble derivatives of APP are produced by proteolytic cleavage of APP within the j] (A4) amino-acid sequence but APP can also be cleaved... 

Figure 18.2 Production of senile plaque (S/A4 amyloid protein. Amyloid fS4 protein (/S/A4) is part of a 695, 751 or 770 amino-acid amyloid precursor protein APP. This is a transmembrane protein which is normally cleared within the fi/A4 amino acid sequence to give short 40 amino-acid soluble derivatives. It seems that under some circumstances as in Alzheimer s disease, APP is cleared either side of the fi/A4 sequence to release the 42/43 amino acid P/A4 which aggregates into the amyloid fibrils of a senile plaque (a). (See also Fig. 18.5.) Some factors, e.g. gene mutation, must stimulate this abnormal clearage leading to the deposition of P/A4 amyloid protein as plaques and tangles and the death of neurons (b)...

Multiple development techniques using stepwise solvent gradients enable a subset of optimal separation conditions to be used to separate a mixture of wide polarity that cannot be separated using a single mobile phase (117,119,120,125). As an example of this approach the separation of 20 common protein amino acid PTH-derivatives is shorn in Figure 7.12 (126). Five... 

Glycine is in a class by itself. It is the only protein amino acid that is not chiral. It is neither hydrophilic nor hydrophobic. With the exception of proline, all other protein amino acids are derived from it by substituting various groups on the oi carbon atom. Glycine is an important inhibitory neurotransmitter in the central nervous system. 

In plants, this non-protein amino acid is derived from L-glutamate and in animals from L-arginine. Moreover, Figure 23 demonstrates that synthesis of alkaloids is complicated by the ability of the same amino acid to synthesize many different alkaloids. 

Kempe M, Mosbach K. Chiral recognition of N alpha-protected amino acids and derivatives in non-covalently molecularly imprinted polymers. Int J Peptide Protein Res 1994 44 603 -606. 

In addition to the 20 common amino acids, proteins may contain residues created by modification of common residues already incorporated into a polypeptide (Fig. 3-8a). Among these uncommon amino acids are 4-hydroxyproline, a derivative of proline, and 5-hydroxylysine, derived from lysine. The former is found in plant cell wall proteins, and both are found in collagen, a fibrous protein of connective tissues. 6-N-Methyllysine is a constituent of myosin, a contractile protein of muscle. Another important uncommon amino acid is y-carboxyglutamate, found in the bloodclotting protein prothrombin and in certain other proteins that bind Ca2+ as part of their biological function. More complex is desmosine, a derivative of four Lys residues, which is found in the fibrous protein elastin. 

Histidine Constitutes a Family of One Nonprotein Amino Acids Are Derived from Protein Amino Acids... 

Aprotinin is a polypeptide consisting of 58 amino acid residues derived from bovine lung tissues and shows inhibitory activity toward various proteolytic enzymes including chymo-trypsin, kallikrein, plasmin, and trypsin. It was also one of the first enzyme inhibitors used as an auxiliary agent for oral (poly)peptide administration. The co-administration of aprotinin led to an increased bioavailability of peptide and protein drugs [5,44,45], The Bowman-Birk inhibitor (71 amino acids, 8 kDa) and the Kunitz trypsin inhibitor (184 amino acids, 21 kDa) belong to the soybean trypsin inhibitors. Both are known to inhibit trypsin, chymotrypsin, and elastase, whereas carboxypeptidase A and B cannot be inhibited [7,46],... 

It is obvious that it is prudent to check the correctness of the amino acid sequence derived from the base sequence of the gene not only at the NHg and COOH termini, which is the common practice, but throughout the entire protein. This would help to uncover any significant errors as well as address the possibility of post-translational modifications. 

Early studies on amino acid/peptide derived amphiphiles revealed that their ability to assemble into various architectures was controlled by surprisingly small structural differences. The hydrophobic residues in the peptide amphiphiles have shown to shield themselves from water and to self-assemble in a manner similar to the protein folding. The similarity of their self-assembling properties to those of proteins, initiated numerous studies for the determination of the relationship between the structure of an individual amino acid or a specific peptide sequence and the resulting architecture. 

Proteins are natural polymers composed of a-amino acids linked by amide (peptide) bonds. Except for glycine (aminoacetic acid), protein-derived amino acids are chiral and have the L configuration. Table 17.1 lists the names, one- and three-letter abbreviations, and structures of the 20 common amino acids. Of these, eight (the essential amino acids) cannot be synthesized in the bodies of adult humans and must be ingested in food. 

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