Threonine isoelectric point

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. 

PSA is a single-chain glycoprotein that is 7% carbohydrate. It has 237 amino acid residues and four carbohydrate side chains with linkages at amino acid 45 (asparagine), 69 (serine), 70 (threonine), and 71 (serine). The N-terminal amino acid is isoleucine, and the C-terminal residue is proline. Its MW is 28,430, and it has isoelectric points from 6.8 to 7.2 because of its various isoforms. The three-dimensional structure and the antigenic domain of PSA have been characterized. ... 

The ability of various diaminopyrimidines to distinguish between analogous forms of the enzyme dihydrofolate reductase is the basis of some of the best contemporary anti-malarial and anti-bacterial therapy (see Section 4.0, p. 123, Tables 4.1 and 4.2, and Section 9.3.3 and 9.6). Let us first look at the differences that exist between various vertebrate types of the enzyme, none of which is much inhibited by trimethoprim (4.P), and then proceed to invertebrate types, which are highly susceptible to this drug. The enzyme from chicken liver has only 75% identity of amino acid sequence with that from ox liver. Moreover, methylmercuric hydroxide activates the avian type twelvefold whereas it inactivates the bovine type. The avian type is much richer in basic amino acids and has an isoelectric point of 8.4 compared to 6.8 for the bovine type. This result is achieved in the avian type by the presence of lysine at positions 32,106, and 154, whereas the bovine type has glycine, threonine, and glutamic acid, respectively, in these positions (Kumars/a/., 1980). 

---