Question

Determine the isoelectric pH for threonine, aspartic acid, arginine, and the tripeptide his-ile-lys. You will probably have to write out the equations in order to do this correctly.

Answer 1

pH for threonine

Threonine

L-Threonine is a neutral, genetically coded amino acid. It is essential in human nutrition.

Symbol

thr t

Molecular formula

C₄H₉NO₃

Molecular weight

119.12

Isoelectric point (pH)

5.64

pK_a values

2.15, 9.12

Aspartic acid (abbreviated as Asp or D) is an ?-amino acid with the chemical formula HOOCCH(NH₂)CH₂COOH. The carboxylate anion and salts of aspartic acid are known as aspartate. The L-isomer of aspartate is one of the 23 proteinogenic amino acids, i.e., the building blocks of proteins. Its codons are GAU and GAC.

Aspartic acid is, together with glutamic acid, classified as an acidic amino acid with a pK_a of 3.9, however in a peptide the pK_a is highly dependent on the local environment. A pK_a as high as 14 is not at all uncommon. Aspartate is pervasive in biosynthesis. As with all amino acids, the presence of acid protons depends on the residue's local chemical environment and the pH of the solution.

arginine

Arginine abbreviated as Arg or R) is an ?-amino acid. It was first isolated in 1886. The L-form is one of the 20 most common natural amino acids. At the level of molecular genetics, in the structure of the messenger ribonucleic acid mRNA, CGU, CGC, CGA, CGG, AGA, and AGG, are the triplets of nucleotide bases or codons that code for arginine during protein synthesis. In mammals, arginine is classified as a semiessential or conditionally essential amino acid, depending on the developmental stage and health status of the individual.^[3] Preterm infants are unable to synthesize or create arginine internally, making the amino acid nutritionally essential for them.^[4] Arginine was first isolated from a lupin seedling extract in 1886 by the Swiss chemist Ernst Schultze.

tripeptide his-ile-lys

The galactopeptide dendrimer GalAG2 ((?-Gal-OC6H4CO-Lys-Pro-Leu)4(Lys-Phe-Lys-Ile)2Lys-His-Ile-NH2) binds strongly to the Pseudomonas aeruginosa (PA) lectin LecA, and it inhibits PA biofilms, as well as disperses already established ones. By starting with the crystal structure of the terminal tripeptide moiety GalA-KPL in complex with LecA, a computational mutagenesis study was carried out on the galactotripeptide to optimize the peptide-lectin interactions. 25 mutants were experimentally evaluated by a hemagglutination inhibition assay, 17 by isothermal titration calorimetry, and 3 by X-ray crystallography. Two of these tripeptides, GalA-KPY (dissociation constant (K(D))=2.7 ?M) and GalA-KRL (K(D)=2.7 ?M), are among the most potent monovalent LecA ligands reported to date. Dendrimers based on these tripeptide ligands showed improved PA biofilm inhibition and dispersal compared to those of GalAG2, particularly G2KPY ((?-Gal-OC6H4CO-Lys-Pro-Tyr)4(Lys-Phe-Lys-Ile)2Lys-His-Ile-NH2). The possibility to retain and even improve the biofilm inhibition in several analogues of GalAG2 suggests that it should be possible to fine-tune this dendrimer towards therapeutic use by adjusting the pharmacokinetic parameters in addition to the biofilm inhibition through amino acid substitutions.