Tyrosine isoelectric point

I 21.10 Predict whether the isoelectric points for the following a-amino acids are considerably acidic, slightly acidic, or basic (a) alanine, (b) lysine, (c) aspartic acid, (d) cystine, (e) tyrosine. (See Table 21-1 and Problem 21.6.) ... 

A more strongly acidic solution is needed to repress this ionization. Aspartic acid s isoelectric point is strongly acidic (pH = 2.7). (d) Cystine is a diaminodicarboxylic acid and behaves like a monoaminomonocarboxylic acid. The isoelectric point is slightly acid (pH = 4.6). (e) Tyrosine is a monoaminomonocarboxylic acid containing a phenolic OH, which however is too weakly acidic to ionize to any significant extent. The isoelectric point is slightly acidic (pH = S.6). 

The properties of the isolated peptides were quite similar in nature, whereby each peptide consisted of 12 amino acids in length and possessed a munber of residues with functional side groups that could stabilize nanoclusters. In many instances, these side chains were the hydroxyl-terminated side chains of serine, threonine, and tyrosine. In two of the peptides (AG3 and AG4), the location of the hydroxylated amino acids was conserved within two of the peptides. Similarly, one proline amino acid was conserved throughout all three of the sequences. Upon incubating each peptide in a solution of silver nitrate with no exogenous reductant, a clearly observable plasmon resonance peak arose at 440 nm for AG3 and AG4, but not with AG5. The peak was quite broad, indicative of a disperse size and shape distribution. The main difference between the active peptides and inactive AG5 was an overall basic isoelectric point for AGS The assays were performed at neutral conditions which would modulate the side-chain dynamics under acidic or basic conditions. 

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. 

When the amino acids are transformed into salts by addition of strong acid or base they all become very soluble. The change in solubility takes place at pH values corresponding to the pK values indicating change from charge zero to +1 or -1. Therefore, tyrosine is insoluble not only at its isoelectric point (pH 5.7) but also in the whole pH interval in which the uncharged form is predominant (pH 3.5-8.0). 

The isoelectric point of tyrosine is 5.63. Toward which electrode does tyrosine migrate during paper electrophoresis at pH 7.0 ... 

On paper electrophoresis at pH 7.0 (more basic than its isoelectric point), tyrosine has a net negative charge and migrates toward the positive electrode. 

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