Amino-acid residues lysine

As discussed, histones are an integral part of nucleo-somes, the basic repeating structural unit of chromatin. The amino termini of histone proteins can be modified post-translationally by processes that include acetylation, methylation, phosphorylation, and ubiquination. Acetylation of the lysines on the amino termini of histones H3 and H4 by histone acetyltransferases decreases histone-DNA interaction and improves the accessibility of DNA to transcriptional activation. On the contrary, histone deacetylation by histone deacetylases promotes the formation of compact nucleo-somes, leading to repression of transcription. Histone deacetylation is in fact a key component to the assembly of heterochromatin, the transcriptionally inactive chromatin. Methylation of the ninth amino acid residue, lysine, on histone H3 generates a binding site for heterochromatin protein (HP 1) and thus is another key event in heterochromatin formation. Phosphorylation of the tenth amino acid, serine, on histone H3 is important for chromosome condensation and mitosis. 

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. 

Besides all the sensory and texturizing properties, GA has interesting antioxidant properties such as an efficient capacity for deactivation of excited electronic states and moderated radical scavenging capacity. There is increasing experimental evidence that associate the antioxidant function with its protein fraction, mainly by amino acid residues such as histidine, tyrosine and lysine, which are generally considered as antioxidants molecules (Marcuse, 1960,1962 Park et al., 2005). 

Note The amino acid residues of lysine (K) and arginine (R) which may be responsible for the binding of POs to polysaccharides are in bold. According to Demand et al. (2002), the mutual substitution of these amino acids has no influence on the sorption properties of the ATg08770 PO of Arabidopsis with pectins, and the deletion of the fragment results in the loss of this function. 

Neurotoxins present in sea snake venoms are summarized. All sea snake venoms are extremely toxic, with low LD5Q values. Most sea snake neurotoxins consist of only 60-62 amino acid residues with 4 disulOde bonds, while some consist of 70 amino acids with 5 disulfide bonds. The origin of toxicity is due to the attachment of 2 neurotoxin molecules to 2 a subunits of an acetylcholine receptor that is composed of a2 6 subunits. The complete structure of several of the sea snake neurotoxins have been worked out. Through chemical modification studies the invariant tryptophan and tyrosine residues of post-synaptic neurotoxins were shown to be of a critical nature to the toxicity function of the molecule. Lysine and arginine are also believed to be important. Other marine vertebrate venoms are not well known. 

As mentioned earlier, glycophorin B carries the N and the Ss blood-group antigens. It is known that the first 26 residues of the amino acid sequence are identical to those in the N-terminal portion of glycophorin A". Moreover, relative to glycophorin A, it has a shortened amino acid chain, comprising 35 amino acid residues at the C-terminus. It is also known to contain 4 lysine residues. 

The possible role that the lysine residues, N-terminal amino acid residues, and carbohydrate residues may play in the display of the MN blood-group determinants by glycophorins A, A, and has been investigated. Assuming that the N-terminal amino acid in each of these glycoproteins plays a prominent role in the display of the MN blood-group determinant, labels were placed on the N-terminal amino acid residues of the glycoproteins. 

Although the order of affinity of PF-4 for different glycosaminogly-cans, and dissociation of their complexes with salts, are typical of nonspecific, electrostatic interactions, PF-4 is not strictly a cationic protein.452 It is probable that heparin binds to clusters of basic amino acids (two lysine pairs) near the carboxyl terminal of a polypeptide chain that has an overall preponderance of acidic amino acid residues.457 High-molecular-weight heparin species can bind two PF-4 molecules, with formation of complexes 10 to 100 times as strong as those with antithrombin.217... 

Chemical modifications of proteins (enzymes) by reacting them with iV-acylimidazoles are a way of studying active sites. By this means the amino acid residues (e.g., tyrosine, lysine, histidine) essential for catalytic activity are established on the basis of acylation with the azolides and deacylation with other appropriate reagents (e.g., hydroxylamine). 

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