What is the pKa for the side chain of arginine?
| Amino acid | pKa1 | pKa2 |
|---|---|---|
| Aspartic acid | 1.88 | 9.60 |
| Glutamic acid | 2.19 | 9.67 |
| Lysine | 2.18 | 8.95 |
| Arginine | 2.17 | 9.04 |
What is the pKa value of arginine?
| Amino Acid | Abbreviation | pKa (25 °C) |
|---|---|---|
| Arginine | Arg | 8.99 |
| Asparagine | Asn | 8.72 |
| Aspartic Acid | Asp | 9.90 |
| Cysteine | Cys | 10.70 |
Why does arginine have high pKa?
Sometimes the amino acid side chain contains a basic group. Examples are histidine, lysine and arginine. The higher the pKa of the conjugate acid, the more tightly the proton is held, and so the more basic the nitrogen atom. Arginine is by far the most basic and histidine is the least basic.
How does pKa affect amino acids?
At a pH below the pKa for each functional group on the amino acid, the functional group is protonated. At a pH above the pKa for the functional group it is deprotonated. If the pH equals the pKa, the functional group is 50% protonated and 50% deprotonated.
What is the side chain of arginine?
Arginine’s side chain is amphipathic, because at physiological pH it contains a positively charged guanidinium group, which is highly polar, at the end of a hydrophobic aliphatic hydrocarbon chain.
Is arginine charged at pH 7?
5. At pH 7, Arg has a fully protonated side chain and is capable of being only a hydrogen bond donor (see Stryer, p. 33). Any amino acid side chain capable of accepting a hydrogen bond can hydrogen bond with Arg at pH = 7….
| Amino Acid | Arginine |
|---|---|
| charge at pH 2 | +1 |
| charge at pH 7 | +1 |
| charge at pH 12 | +1 (50%) |
What is pKa of amino acids?
Amino acids by themselves have amino (pKa ~9.0-10.5) and carboxyl groups (pKa ~2.0-2.4) that can be titrated. At neutral pH the amino group is protonated, and the carboxyl group is deprotonated. The side chains of acid and basic amino acids, and some polar amino acids can also be titrated: Amino acid.
Why do amino acids have different pKa values?
pKa is the negative base-10 logarithm of the acid dissociation constant of a solution. Therefore it is essentially affected by the pH of a solution. The amino acids contain a COOH and a NH2 group. And the conformation of these charged groups in turn is decided by the pH of the surrounding microenvironment or solution.
What happens when pKa pH?
Increase in pH Remember that when the pH is equal to the pKa value, the proportion of the conjugate base and conjugate acid are equal to each other. As the pH increases, the proportion of conjugate base increases and predominates.
What does pKa tell us about amino acids?
The pKa value given for the amino group on any amino acid specifically refers to the equilibrium between the protonated positive nitrogen and deprotonated neutral nitrogen. You’ll never see a neutral nitrogen deprotonated to form a negative on an amino acid.
What is the structure of arginine?
C6H14N4O2
Arginine/Formula
Why is the pKa of arginine always low?
That is, due to an energetic penalty of Δ Go = 2.303RT (Δp Ka ), the p Ka of an arginine might never be perturbed to a value as low as 7 because the host proteins would unfold owing to the associated loss of net stability. 17 In this respect, the properties of the lysine side chain are very different.
What is the pKa value of arginine guanidinium?
Using complementary approaches of potentiometry and NMR spectroscopy, we have determined that the equilibrium acid dissociation constant (p Ka value) of the arginine guanidinium group is 13.8 ± 0.1. This is substantially higher than that of ∼12 often used in structure-based electrostatics calculations and cited in biochemistry textbooks.
What is the pKa of the are group of lysine?
The R-group of lysine has a pKa of about 10.5 so it is positively charged. The R-Groups of both aspartic acid and glutamic acid have a pKa of about 4 so they are both negatively charged. So, there are a total of two positive charges, one contributed the alpha amino alanine and one contributed by the R-group of lysine.
What are the PKA and pi values of amino acids?
pKa and pI values of amino acids Amino acid 3-letter code 1-letter code pKa Cα-COOH pKa Cα-NH 3 + pKa side chain Isoelectric point (pI) Alanine Ala A 2.34 9.69 – 6.02 Arginine Arg R 2.17 9.04 12.48 10.76 Asparagine Asn N 2.02 8.80 – 5.41 Aspartic acid Asp D 2.09 9.82 3.86 2.98 Cysteine Cys C 1.71 10.78 8.33 5.02