Alanine tetrapeptide

Czerminski and Elber [64], who generated an almost complete map of the minima and barriers of an alanine tetrapeptide in vacuum. Using the master equation approach they were able to smdy aspects of this system s kinetics, which involve the crossing of barriers of different heights. 

R. A. DiStasio, Jr. R. P. Steele, Y. M. Rhee, Y. Shao, and M. Head-Gordon, J. Comput. Chem., 28, 839-859 (2007). An Improved Algorithm for Analytical Gradient Evaluation in Resolution-of-the-Identity Second-Order Moller-Plesset Perturbation Theory Application to Alanine Tetrapeptide Conformational Analysis. 

Ammo acid analysis of a certain tetrapeptide gave alanine... 

The sequence of each different peptide or protein is important for understanding the activity of peptides and proteins and for enabling their independent synthesis, since the natural ones may be difficult to obtain in small quantities. To obtain the sequence, the numbers of each type of amino acid are determined by breaking down the protein into its individual amino acids using concentrated acid (hydrolysis). For example, hydrolysis of the tetrapeptide shown in Figure 45.3 would give one unit of glycine, two units of alanine, and one unit of phenylalanine. Of course, information as to which amino acid was linked to which others is lost. 

In the course of studies on aminoaciduria in Fanconi s syndrome, Dent (Dl) isolated from the urine of the subject investigated a simple peptide identified as serylglycylglycine. Carsten (Cl) found in normal urine several peptides containing in every case one of the dicarboxylic amino acids. He discovered also two tetrapeptides, one of them consisting of equimolar amounts of aspartic acid and glycine, and the second composed of glycine, alanine, and glutamic acid in the ratio 2 1 1. The first of these tetrapeptides was also found in the urine of a patient with rheumatoid arthritis. 

Other cyclic tetrapeptides have also been isolated by Japanese workers and AM toxins I, II, and III, isolated from Alternaria mail., are extremely toxic to certain plant species (9.10). These are constructed of L- i-hydroxyisovaleric acid, L-alanine, c-amino-acrylic acid and, in AM toxin I, L-6(-amino- -( .-methoxyphenyl)-valeric acid. The phenyl residue in AM toxin II is L-t(-amino-S-phenylvaleric acid, while in AM toxin III, it is L-ol-amino-( .-hydroxyphenyl)valeric acid (Figure 2), All the AM toxins produce leaf spot, or necrosis, in apple but as might he expected slight change in substitution (R-group) on the phenyl ring radically alters the specific activity of the molecule. Both AM toxin I and III induce interveinal necrosis in the "Indo" apple cultivar, which is also highly susceptible to A. mail. at concentrations as low as 0.1 pph within 18 h after treatment. In contrast, the resistant apple cultivar "Jonathan" is only affected by 1 ppm of AM toxin I and 10 ppm of AM toxin III. 

Taste of Orn-p-Ala Derivatives. We reported in the previous paper (5) that omithyl-p-alanine monohydrochloride produced the salty taste as omithyltaurine. We prepared two tetrapeptides composed of ornithine and p-alanine. Both tetrapeptides, however, produced mainly an astringent taste instead of the salty or the umami taste (Table Xffl). 

You have a peptide that is a potent inhibitor of nerve conduction and you wish to obtain its primary sequence. Amino acid analysis reveals the composition to be Ala(5) Lys Phe. Reaction of the intact peptide with FDNB releases free DNP-alanine on acid hydrolysis. e-DNP-lysine (but not a-DNP-lysine) is also found. Tryptic digestion gives a tripeptide (composition Lys, Ala (2)) and a tetrapeptide (composition Ala(3), Phe). Chymotryptic digestion of the intact peptide releases a hexapeptide and free alanine. Derive the peptide sequence. 

From a rare fungus you have isolated an octapeptide that prevents baldness, and you wish to determine the peptide sequence. The amino acid composition is Lys(2), Asp, Tyr, Phe, Gly, Ser, Ala. Reaction of the intact peptide with FDNB yields DNP-alanine plus 2 moles of e-DNP-lysine on acid hydrolysis. Cleavage with trypsin yields peptides the compositions of which are (Lys, Ala, Ser) and (Gly, Phe, Lys), plus a dipeptide. Reaction with chymotrypsin releases free aspartic acid, a tetrapeptide with the composition (Lys, Ser, Phe, Ala), and a tripeptide the composition of which, following acid hydrolysis, is (Gly, Lys, Tyr). What is the sequence ... 

How many tetrapeptides containing alanine, serine, leucine, and glutamic acid do you think there are Use the three-letter abbreviations to name three. 

Twenty-four tetrapeptide combinations are possible for the four amino acids alanine (A), glycine (G), phenylalanine (F), and valine (V). Remember that the order is important AG is not the same peptide as GA. Using the one-letter abbreviations for each amino acid the possibilities are... 

Figure A2.2 The structure of the monomer unit of the polyglycan of S. aureus. The cross links between chains are from the y-amino group of the lysine to the carboxylate of the C-terminal D-alanine. The tetrapeptide can contain other amino acid residues...

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