Amino-acid residues phenylalanine

For example, chymotrypsin cleaves peptides on the C-terminal side of aromatic amino acid residues phenylalanine, tyrosine, and tryptophan, and to a lesser extent some other residues with bulky side-chains, e.g. Leu, Met, Asn, Gin. On the other hand, trypsin cleaves peptides on the C-terminal side of the basic residues arginine and lysine. Elastase usually catalyses hydrolysis of peptide bonds on the C-terminal side of neutral aliphatic amino acids, especially glycine or alanine. These three pancreatic enzymes are about 40% identical in their amino acid sequences, and their catalytic mechanisms are nearly identical. 

A globular protein in aqueous surroundings contains the following amino acid residues phenylalanine, methionine, glutamate, lysine, and alanine. Which amino acid side chains would be directed toward the inside of the protein and which would be directed toward the aqueous surroundings ... 

Alanine (ala) Phenylalanine (phe) R 1 0 - HNCHC N General formula for an amino acid residue Aspartic Acid (asp)... 

The specific ribonucleotide sequence in mRNA forms a message that determines the order in which amino acid residues are to be joined. Each "word," or codon, along the mRNA chain consists of a sequence of three ribonucleotides that is specific for a given amino add. For example, the series UUC on mRNA is a codon directing incorporation of the amino acid phenylalanine into the growing protein. Of the 43 = 64 possible triplets of the four bases in RNA, 61 code for specific amino acids and 3 code for chain termination, fable 28.1 shows the meaning of each codon. 

Concerning the Ca2+-triggered luminescence of obelin, Deng et al. (2001) reported an interesting observation (Fig. 4.2.2) the luminescence of the recombinant obelin from O. longissima is blue (7max 475 nm), whereas a mutant of this obelin, in which the amino acid residue-92 has been changed from tryptophan to phenylalanine, emits... 

Boehm et al.100 have synthesised and studied a series of half-sandwich rhodium (III) and iridium (III) complexes, derivatives of salicylaldehyde and L-amino acid esters. The diastereoselectivity has shown strong dependence on the type of metal as well as amino acid residue. The labile configuration of the metal atoms was suggested because of changes in the diastereomers ratio with increasing temperature. Fast epimerisation at the metal atom was suggested for some S-phenylalanine complexes. 

By means of a procedure described above, Hanson and Fittkau (HI) isolated seventeen different peptides from normal urine. One of them, not belonging to the main peptide fraction, consisted of glutamic acid, and phenylalanine with alanine as the third not definitely established component. The remaining peptides contained five to ten different amino acid residues and some unidentified ninhydrin-positive constituents. Four amino acids, i.e., glutamic acid, aspartic acid, glycine, and alanine, were found in the majority of the peptides analyzed. Twelve peptides contained lysine and eight valine. Less frequently encountered were serine, threonine, tyrosine, leucine, phenylalanine, proline, hydroxyproline, and a-aminobutyric acid (found only in two cases). The amino acid composi-... 

The actual information transfer is based on the interaction between the mRNA codons and another type of RNA, transfer RNA (tRNA see p. 82). tRNAs, of which there are numerous types, always provide the correct amino acid to the ribosome according to the sequence information in the mRNA. tRNAs are loaded with an amino acid residue at the 3 end. Approximately in the middle, they present the triplet that is complementary to each mRNA codon, known as the anticodon (GAA in the example shown). If the codon UUC appears on the mRNA, the anticodon binds a molecule of Phe-t-RNA to the mRNA (5) and thus brings the phenylalanine residue at the other end of the molecule into a position in which it can take over the growing polypeptide chain from the neighboring tRNA (6). 

A specialized amino acid residue that serves as an essesn-tial electrophilic center in several enzymatic reactions, including those catalyzed by L-phenylalanine ammonia lyase (Reaction L-phenylalanine tranx-cinnamate + NH3) and L-histidine ammonia lyase (Reaction L-histi-dine urocanate + NH3). The former facilitates the elimination of ammonia and the pro-S hydrogen of phe-nylanine, and the initial step is nucleophilic attack of... 

In 1970s, first application of metal-chelate affinity chromatography which is later named as "immobilized-metal (ion) affinity chromatography (IMAC) was perfomed. Metal-chelate chromatography technique exploits selective interactions and affinity between transition metal immobilized on a solid support (resin) via a metal chelator and amino acid residues which act as electron donors in the protein of interest [25-26]. As well as aromatic and heterocyclic compounds, proteins such as histidine, tyrosine, tyriptophane and phenylalanine posses affinity to transition metals which form complexes with compounds rich in electrons [25,27]. 

No generalizations can be made about the molecular weights of biologically active peptides and proteins in relation to their functions. Naturally occurring peptides range in length from two to many thousands of amino acid residues. Even the smallest peptides can have biologically important effects. Consider the commercially synthesized dipeptide L-aspartyl-L-phenylalanine methyl ester, the artificial sweetener better known as aspartame or NutraSweet. 

A number of other racemases and epimerases may function by similar mechanisms. While some amino acid racemases depend upon pyridoxal phosphate (Chapter 14), several others function without this coenzyme. These include racemases for aspartate,113 glutamate,114-1153 proline, phenylalanine,116 and diamino-pimelate epimerase.117 Some spiders are able to interconvert d and l forms of amino acid residues in intact polypeptide chains.118119... 

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