Amino Acid pKa Values and Side Chain Identities Amino Acid pKa Values α-CO 2H α-NH 3+ Side Side Chain (Z) – “fully” protonated Alanine 2.34 9.69 –CH 3 Arginine 2.17 9.04 12.48 H 2NCNHCH 2CH 2CH 2Ð NH2 Asparagine 2.02 8.84 H2NCCH2Ð O Aspartic Acid 2.09 9.82 3.86 –CH 2CO 2H Cysteine 1.71 10.78 8.33 –CH 2SH
Amino acid pK a values. pK a values of amino acid side chains play an important role in defining the pH-dependent characteristics of a protein. The pH-dependence of the activity displayed by enzymes and the pH-dependence of protein stability, for example, are properties that are determined by the pK a values of amino acid side chains.
The individual amino acids all have slightly different pKa values and therefore have different isoelectric points. For amino acids with charged side chains, the pKa of the side chain is involved. Thus for Asp or Glu with negative side chains, pI = ½(pKa 1 + pKa R), where pKa R is the side chain pKa.
Amino acids differ from each other with respect to their side chains, which are referred to as R groups. The R group for each of the amino acids will differ in structure, electrical charge, and polarity. Refer to the charts and structures below to explore amino acid properties, types, applications, and availability.
this standard classification scheme for amino acid side-chains. Glycine has the smallest side-chain (a hydrogen), and is the only non-chiral amino acid. Because it effectively lacks a side-chain, glycine has much less steric hindrance than the other amino acids. In addition, because it effectively lacks a side-chain, the glycine side-
Two amino acids have acidic side chains at neutral pH. These are aspartic acid or aspartate (Asp) and glutamic acid or glutamate (Glu). Their side chains have carboxylic acid groups whose pKa's are low enough to lose protons, becoming negatively charged in the process.
www.chem.purdue.edu/courses/chm333/Spring 2013/Lectures/Spring 2013 Lecture 7...
Amino Acids as Acids, Bases and Buffers: - Amino acids are weak acids - All have at least 2 titratable protons (shown below as fully protonated species) and therefore have 2 pKa’s o α-carboxyl (-COOH) o α-amino (-NH 3 +) - Some amino acids have a third titratable proton in the R group and therefore a third pKa o Showing all protonated ...
2) find the number of basic amino acids in that polypeptide chain (let's say you have "nb" basic amino acids - you could also have no basic amino acids in your chain, in which case nb=0), 3) now, the PI is found by averaging the pKa #nb+1 and pKa #nb+2 from the list you made in the first step.
All AAs have at least two ionizable groups, each with its own acid dissociation constant (pKa). pKa of the α-carboxyl group = 2; pKa of the α-amino group = 9–10; Acidic/basic AAs have another pKa for their ionizable side chain group, which varies. Acidic amino acids: Side groups are negatively charged at body pH (both have a pKa of ∼ 4 ...
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