Arginine isoelectric point

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... 

Problem 21.43 What occurs when an electric current is passed through an aqueous solution, buffered at pH = 6.0, of alanine (6.0), glutamic acid (3.2). and arginine (10.7) The isoelectric points are shown in parentheses. ... 

Ornithine (Qrn) with an isoelectric point of 9,7 was isolated by Riesser in 1906 from arginine. It has the formula... 

Calculate the isoelectric point for histidine, aspartic acid, and arginine. Calculate the fractional charge for... 

NE is a basic protein due to the large number of arginine residues and has an isoelectric point between 10 and 11 1251. There are at least three iso-forms of NE, which can be separated by isoelectric focusing or by polyacrylamide gel electrophoresis. The istfonns have identical N-terminal sequences and similar catalvtie activity and are believed to arise from minor differences in two N-linked carbohydrate side chains. The major form contains about 22% carbohydrate. 

Basic amino acids (histidine, lysine, and arginine) have isoelectric points at pH values of 7.6, 9.7, and 10.8, respectively. These values reflect the weak basicity of the imidazole ring, the intermediate basicity of an amino group, and the strong basicity of the guanidino group. A basic solution is needed in each case to prevent protonation of the basic side chain to keep the amino acid electrically neutral. 

Draw the resonance forms of a protonated guanidino group, and explain why arginine has such a strongly basic isoelectric point. 

Metabolism of arginine produces urea and the rare amino acid ornithine. Ornithine has an isoelectric point close to 10. Propose a structure for ornithine. 

The extent of ADP-ribosylation is checked by separating modified and unmodified actin using non-denaturing gel electrophoresis, whereas SDS gel electrophoresis is not efficient. ADP-ribosylation changes the isoelectric point of actin to more acid values, resulting in increased migration. This method is also appropriate to study double or triple ADP-ribosylation of actin, e.g., in the presence of iota toxin and/or turkey erythrocyte transferase (Just ef al., 1995). The latter transferase modifies actin even at two arginine residues. 

The high isoelectric point suggests a strongly basic side chain as in lysine. The N—CH2 bond in the side chain of arginine is likely to have remained intact during the metabolism. (Can you propose a likely mechanism for this reaction )... 

Figure 10.11 summarizes the measurements for 15 different amino acids. The order of the amino acids is according to their isoelectric points. Interestingly, cyclopeptide 2 is almost not sensitive, whereas the coating with cyclopeptide 1 can discriminate significantly between amino acids of acidic, neutral or basic character. L-Lysine and L-arginine show the strongest interactions, but the response is different between these two amino acids. This strong interaction could be due to direct ionic interactions between amino acid, cyclopeptide 1 and phosphate ions. When we used protected derivatives of lysine and arginine, we were able to confirm that the interaction between 1 and lysine or arginine is mainly dependent on the basic groups of these amino acids (Fig. 10.12). While esterifica-...

Table 4 examines the amino acid composition of purified SCP2 [21] and compares it with the amino acid compositions of 3 other preparations of interest [47-49], The most abundant amino acid in purified SCP2 is lysine, which accounts for 14 mole%. Since the isoelectric point for SCPj is approximately 8.6, it follows that a substantial portion of the glutamic and aspartic acid residues are amidated. Also of interest is the finding that SCPj contains no arginine or tyrosine, and only small amounts (perhaps 1 residue each) of histidine and tryptophan. 

Mathematical Galculate the isoelectric point of each of the following amino acids glutamic acid, serine, histidine, lysine, tyrosine, and arginine. 

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