Amino acids C-terminal

Identify the N terminal and the C terminal amino acid m the original peptide and m each fragment... 

P-Endorphin. A peptide corresponding to the 31 C-terminal amino acids of P-LPH was first discovered in camel pituitary tissue (10). This substance is P-endorphin, which exerts a potent analgesic effect by binding to cell surface receptors in the central nervous system. The sequence of P-endorphin is well conserved across species for the first 25 N-terminal amino acids. Opiates derived from plant sources, eg, heroin, morphine, opium, etc, exert their actions by interacting with the P-endorphin receptor. On a molar basis, this peptide has approximately five times the potency of morphine. Both P-endorphin and ACTH ate cosecreted from the pituitary gland. Whereas the physiologic importance of P-endorphin release into the systemic circulation is not certain, this molecule clearly has been shown to be an important neurotransmitter within the central nervous system. Endorphin has been invaluable as a research tool, but has not been clinically useful due to the avadabihty of plant-derived opiates. 

These methodologies have been reviewed (22). In both methods, synthesis involves assembly of protected peptide chains, deprotection, purification, and characterization. However, the soHd-phase method, pioneered by Merrifield, dominates the field of peptide chemistry (23). In SPPS, the C-terminal amino acid of the desired peptide is attached to a polymeric soHd support. The addition of amino acids (qv) requires a number of relatively simple steps that are easily automated. Therefore, SPPS contains a number of advantages compared to the solution approach, including fewer solubiUty problems, use of less specialized chemistry, potential for automation, and requirement of relatively less skilled operators (22). Additionally, intermediates are not isolated and purified, and therefore the steps can be carried out more rapidly. Moreover, the SPPS method has been shown to proceed without racemization, whereas in fragment synthesis there is always a potential for racemization. Solution synthesis provides peptides of relatively higher purity however, the addition of hplc methodologies allows for pure peptide products from SPPS as well. 

The actual process of solid-phase peptide synthesis, outlined in Figure 27.15, begins with the attachment of the C-terminal amino acid to the chloromethylated polymer in step 1. Nucleophilic substitution by the carboxylate anion of an A-Boc-protected C-terminal... 

By successively adding anino acid residues to the C-terminal amino acid, it took Menifield only eight days to synthesize bradykinin in 68% yield. The biological activity of synthetic bradykinin was identical with that of natural material. 

FIGURE 27.19 Proposed mechanism of hydrolysis of a peptide catalyzed by carboxypeptidase A. The peptide is bound at the active site by an ionic bond between its C-terminal amino acid and the positively charged side chain of arginine-145. Coordination of Zn to oxygen makes the carbon of the carbonyl group more positive and increases the rate of nucleophilic attack by water. 

Solid-phase peptide synthesis (Section 27.18) Method for peptide synthesis in which the C-terminal amino acid is covalently attached to an inert solid support and successive amino acids are attached via peptide bond formation. At the completion of the synthesis the polypeptide is removed from the support. 

ENZYMATIC ANALYSIS WITH CARBOXYPEPTIDASES. Carboxypeptidases are enzymes that cleave amino acid residues from the C-termini of polypeptides in a successive fashion. Four carboxypeptidases are in general use A, B, C, and Y. Carboxypeptidase A (from bovine pancreas) works well in hydrolyzing the C-terminal peptide bond of all residues except proline, arginine, and lysine. The analogous enzyme from hog pancreas, carboxypeptidase B, is effective only when Arg or Lys are the C-terminal residues. Thus, a mixture of carboxypeptidases A and B liberates any C-terminal amino acid except proline. Carboxypeptidase C from citrus leaves and carboxypeptidase Y from yeast act on any C-terminal residue. Because the nature of the amino acid residue at the end often determines the rate at which it is cleaved and because these enzymes remove residues successively, care must be taken in interpreting results. Carboxypeptidase Y cleavage has been adapted to an automated protocol analogous to that used in Edman sequenators. 

The heptyl ester was developed as an enzymatically removable protective group for C-terminal amino acid protection. 

The long, repetitive sequence of —N—CH-CO- atoms that make up a continuous chain is called the protein s backbone. By convention, peptides are written with the N-terminal amino acid (the one with the free -NH3 1 group) on the left and the C-terminal amino acid (the one with the free -C02 group) on the right. The name of the peptide is indicated by using the abbreviations listed in Table 26.1 for each amino add. Thus, alanylserine is abbreviated Ala-Ser or A-S, and serylalanine is abbreviated Ser-Ala or S-A. Needless to say, the one-letter abbreviations are more convenient than the older three-letter abbreviations. 

C-terminal amino acid (Section 26.4) The amino acid with a free -C02H group at the end of a protein chain. 

Two isotypes of SUR have been cloned, SUR1 and SUR2. In addition, two splicing variants of SUR2, distinguished by 42 C-terminal amino acids, have been... 

The common C-terminal amino acid sequence required for exerting activity at tachykinin receptors is shown in bold endokinin C and D lack the C-terminal Met and are almost devoid of affinity at these receptors. In red, the sequence of neurokinin A of which neuropeptide-gamma and neuropeptide-kappa are elongated forms and neurokinin A (3-10) is a product of beta or gamma-TAC1 mRNAs or an NKA metabolite active at tachykinin receptors. In blue, the sequence of human HK-1 of which endokinin A and B are elongated forms. 

Peptide synthesis was amenable to solid-phase techniques since the process was repetitive. The C-terminal amino acid is attached to polymeric surface and the peptide chain is assembled via a two-step process coupling of the incoming amino acid that has the alpha-amino group protected... 

A good way to start sequencing is to begin near the precursor mass. Mass differences between precursor and first ions in C- and N-terminal series are specific to the ion series. Using this approach, we may be able to identify first N- and C-terminal amino acids, respectively. 

High-voltage electrophoresis and subsequent paper chromatography of the fractions obtained made possible the isolation from the analyzed mixture of twenty-two components giving colored spots with ninhydrin and isatin. Among these, fourteen were identified as peptides and their amino acid composition established (Table 5). In the case of eight peptides, also N- and C-terminal amino acids were determined (Table 6). 

Peptide V-terminal amino acid C-terminal amino acid... 

Like other peptides, the ability of SP to stimulate histamine release is closely related to its ability to mobilize Ca from a cellular pool and to the basic and the hydrophobic properties of its N-terminal and C-terminal amino acids, respectively. In this regard, intact SP (SP, n) is more active than the N-terminal tetrapeptide (SP8 n) with SP,, giving a half-maximal response at 8 x 10 6M and 1 x 10 5 M producing some 40% release [99], The C-terminal heptapeptide, SP, 6 was inactive [99],... 

In their initial studies on the effects of vasoactive peptides on mast-cell secretion, Johnson and Erdos [31] concluded that the ability of peptides to elicit a secretory response from mast cells depended upon the number of basic groups a peptide contained, and not on the structure of the N-terminal or C-terminal amino acids per se. They found, for example, that Polistes kinin, with... 

Figure 4.11. Comparison of the histamine-releasing activity of three fragments of SP with decreasing numbers of C-terminal amino acids 199] , SP, n O, SP, s A, SP, 7 , SP, s.

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