Terminic acid

Surfactants are prepared which contain carboxylic acid ester or amide chains and terminal acid groups selected from phosphoric acid, carboxymethyl, sulfuric acid, sulfonic acid, and phosphonic acid. These surfactants can be obtained by reaction of phosphoric acid or phosphorus pentoxide with polyhydroxystearic acid or polycaprolactone at 180-190°C under an inert gas. They are useful as polymerization catalysts and as dispersing agents for fuel, diesel, and paraffin oils [69]. 

Ottersbach, K., and Graham, G.J. (2001) Aggregation-independent modulation of proteoglycan binding by neutralization of C-terminal acidic residues in the chemokine macrophage inflammatory protein lalpha. Biochem J. 354, 447-453. 

These results, therefore, attest to the production of oxalic acid from acetic acid via the two pathways indicated and also lend support to the suggested intermediary stages involved in the genesis of the terminal acid. The mechanism of acetate - oxalate formation, consequently, was shown to proceed along the following two pathways ... 

The N-terminal acid is detected with 2,4-dinitrofluorobenzene (dnfb). 

Debus 1 favoured the assumption that the central linking atoms between the terminal acidic groups comprise an oxygen and a sulphur atom ... 

Carboxypeptidase A catalyzes the hydrolysis of carboxyl-terminal acidic or neutral amino acids however, the rate of hydrolysis depends on the structure of the side chain R. Amino acids with nonpolar aryl or alkyl side chains are cleaved more rapidly. Carboxypeptidase B is specific for the hydrolysis of basic COOH-terminal amino acids (lysine and arginine). Neither peptidase functions if proline occupies the COOH-terminal position or is the next to last amino acid. 

Determination of the iV-terminal acid in the peptide can be made by treatment of the peptide with 2,4-dinitrofluorobenzene, a substance very reactive in nucleophilic displacements with amines but not amides (see Section 14-6B). The product is an N-2,4-dinitrophenyl derivative of the peptide which, after hydrolysis of the amide linkages, produces an iV-2,4-dinitrophenyl-amino acid ... 

These amino-acid derivatives can be separated from the ordinary amino acids resulting from hydrolysis of the peptide because the low basicity of the 2,4-dinitrophenyl-substituted nitrogen (Section 23-7C) greatly reduces the solubility of the compound in acid solution and alters its chromatographic behavior. The main disadvantage to the method is that the entire peptide must be destroyed in order to identify the one A-terminal acid. 

Fig. 3. The acidic regions of rgRGS domains. The rgRGS domains consist of a core RGS box, which is homologous in sequence and structure to other RGS domains, a C-terminal extension that helps stabilize the core structure, and an N-terminal acidic region that forms a second binding motif to the a subunit. Amino acids in bold-underline were shown to have contacts with G13a mutations of residues indicated with an arrow could attenuate GAP activity. This acidic region plays a fundamental role in GAP activity, and differences among the RGS-RhoGEFs appear to determine their ability to act as GAPs. See text for details.

While most of peroxidases utilize the distal histidine as a general acid-base catalyst, chloroperoxidese (CPO) uniquely uses glutamate as the terminal acid-base catalyst (Scheme 8) (56). 

Fig. 5. Schematic of end group transformations that have been demonstrated for mono-layers with terminal ester groups. The terminal acid group has been used to couple amino acids to the surface while the branched structure that results from the Grignard reaction is expected to result in more stable, passivated surface.

The reaction of terminal acid functions with glycidyl methacrylate is generally considered to proceed readily and quantitatively. However, Yamashita102) found that some side reactions can occur at elevated temperature, and he proposed another method involving reaction of the terminal carboxy function of the macromolecule with either 2-hydroxyethyl methacrylate or N-methyl-N-2-hydroxyethyl methacrylamide in the presence of bis-isopropylcarbodiimide. This two-step process was shown to proceed quantitatively. The reaction scheme is as follows ... 

Proteins and peptides are linear polymers made up of combinations of the 20 most common amino acids linked with each other by peptide bonds. Moreover, the protein produced by the ribosome may undergo covalent modifications, called post-translational modifications, after its incorporation of amino acids. Over 200 such modifications have been detected already [13,14], the most important being glycosylation, the formation of disulfide bridges, phosphorylation, sulfation, hydroxylation, carboxylation and acetylation of the N-terminal acid [15]. The most frequent are listed in Table 8.1 and a more comprehensive database of mass changes due to post-translational modifications of peptides and proteins is available on the Internet [16]. 

Interpretation of the spectra is based on the mechanisms and the fragmentation pathways described above, as shown by the following example. A CID MS/MS fragment spectrum of a peptide with sequence Gly-Ile-Pro-Thr-Leu-Leu-Leu-Phe-Lys measured at high energy is shown in Figure 8.13. This spectrum contains the complete series of b ions, thus allowing one to deduce the peptide sequence from the N-terminal acid to the C-terminal acid, whereas the series of y ions allows identification of the sequence in the reverse direction. In fact, the mass difference of 97 Da between peak b2 and b3 indicates that the amino acid in position 3 corresponds to a proline (see Table 8.2). Similarly, the 147 Da difference between peaks yi and y2 indicates that, the amino acid in the next-to-last position is a phenylalanine. The m/z values of ions W3, W4, W5 and wg imply that the amino acid in... 

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