Lysine arginine and

Some ammo acids have side chains that bear acidic or basic groups As Table 27 3 indicates these ammo acids are characterized by three values The third pK reflects the nature of the side chain Acidic ammo acids (aspartic and glutamic acid) have acidic side chains basic ammo acids (lysine arginine and histidine) have basic side chains The isoelectric points of the ammo acids m Table 27 3 are midway between the pK values of the zwitterion and its conjugate acid Take two examples aspartic acid and lysine Aspartic acid has an acidic side chain and a pi of 2 77 Lysine has a basic side chain and a pi of 9 74... 

The 20 common amino acids can be further classified as neutral, acidic, or basic, depending on the structure of their side chains. Fifteen of the twenty have neutral side chains, two (aspartic acid and glutamic acid) have an extra carboxylic acid function in their side chains, and three (lysine, arginine, and histidine) have basic amino groups in their side chains. Note that both cysteine (a thiol) and tyrosine (a phenol), although usually classified as neutral amino acids, nevertheless have weakly acidic side chains that can be deprotonated in strongly basic solution. 

There are numerous abnormalities of cysteine metabolism. Cystine, lysine, arginine, and ornithine are excreted in cystine-lysinuria (cystinuria), a defect in renal reabsorption. Apart from cystine calculi, cystinuria is benign. The mixed disulfide of L-cysteine and L-homocysteine (Figure 30-9) excreted by cystinuric patients is more soluble than cystine and reduces formation of cystine calculi. Several metabolic defects result in vitamin Bg-responsive or -unresponsive ho-mocystinurias. Defective carrier-mediated transport of cystine results in cystinosis (cystine storage disease) with deposition of cystine crystals in tissues and early mortality from acute renal failure. Despite... 

The amine containing side chains in lysine, arginine, and histidine typically are exposed on the surface of proteins and can be derivatized with ease. The most important reactions that can occur with these residues are alkylation and acylation (Figure 1.8). In alkylation, an active... 

The amino acids in question are the basic amino acids lysine, arginine, and histidine, and the acidic amino acids aspartic acid and glutamic acid. The side-chain functions of these amino acids, ionized at pH 7 (see Box 4.7), act as acids or bases. In a reverse sequence, protons may be acquired or donated to regenerate the conjugate acids and conjugate bases. 

Dependence of tyrosine, lysine, arginine and ornithine decarboxylase on a phosphorylated pyridoxal derivative shown. 6, 8... 

Some amino acids such as aspartic acid and glutamic acid contain an additional acid functional group, while amino acids such as lysine, arginine, and histidine contain additional basic groups. The presence of these units will confer to the protein tendencies to move toward the anode or cathode. The rate of movement is dependent on a number of factors including the relative abundance and accessibility of these acid and base functional groups. 

Based on the properties of the side chains, the 20 amino acids can be put into six general classes. The first class contains amino acids whose side chains are aliphatic, and is usually considered to include glycine, alanine, valine, leucine, and isoleucine. The second class is composed of the amino acids with polar, nonionic side chains, and includes serine, threonine, cysteine, and methionine. The cyclic amino acid proline (actually, an imino acid) constitutes a third class by itself. The fourth class contains amino acids with aromatic side chains tyrosine, phenylalanine, and tryptophan. The fifth class has basic groups on the side chains and is made up of the three amino acids lysine, arginine, and histidine. The sixth class is composed of the acidic amino acids and their amides aspartate and asparagine, and glutamate and glutamine. 

Cysteine and cystine are relatively insoluble and are toxic in excess.450 Excretion is usually controlled carefully. However, in cystinuria, a disease recognized in the medical literature since 1810,451 there is a greatly increased excretion of cystine and also of the dibasic amino acids.451 452 As a consequence, stones of cystine develop in the kidneys and bladder. Patients may excrete more than 1 g of cystine in 24 h compared to a normal of 0.05 g, as well as excessive amounts of lysine, arginine, and ornithine. The defect can be fatal, but some persons with the condition remain healthy indefinitely. Cystinuria is one of several human diseases with altered membrane transport and faulty reabsorption of materials from kidney tubules or from the small intestine. Substances are taken up on one side of a cell (e.g., at the bottom of the cell in Fig. 1-6) and discharged into the bloodstream from the other side of the cell. In another rare hereditary condition, cystinosis, free cystine accumulates within lyso-somes.453... 

An additional point should be noted from table 3.3. Whereas the amino acid side chains (R groups) that are normally charged at physiological pH are restricted to five amino acids (aspartic acid, glutamic acid, lysine, arginine, and sometimes histidine), a number of potentially ionizable R groups are part of other amino acids. These include cysteine, serine, threonine, and tyrosine. The ionization reac-... 

The charged side chains of lysine, arginine, and histidine form salt bridges with carboxylate groups about 25% of the time. Seven carboxyl-... 

There is no acidic amino acid inc this transit peptide sequence. By contrast, 16% of the total 50 residues are arginines plus lysines, and, if histidines are included, the content of basic residues becomes 26%. The basic nature of the transit peptide is in contrast to the acidic nature of the mature protein the content of aspartic and glutamic acids in the mature protein is much higher than the content of lysine, arginine, and histidine. It seems likely that the acidity of the mature protein molecule is neutralized with the excessive basicity of the transit peptide. 

FIGURE 1. The lysine family of cationic amino acids. Structures include the typical a-amino acid found in proteins, and the cationic side-chains of lysine, arginine and the two substituted lysine derivatives recently found in high abundance in the silaffins occluded within the biosilica of a diatom35. The derivatives with multiple methylaminopropyl units were previously unknown in biological systems... 

The amino acids with basic side chains—lysine, arginine, and histidine—all have pi values greater than 7. In strongly acidic solution they exist in dicationic forms, and all have significant amounts of a cationic form and a dipolar ion present at neutral pH. 

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