What is the pKa of cysteine?
What is the pKa of cysteine?
1.92
| Amino Acid | Abbreviation | pKa (25 °C) |
|---|---|---|
| Cysteine | Cys | 1.92 |
| Glutamic Acid | Glu | 2.10 |
| Glutamine | Gln | 2.17 |
| Glycine | Gly | 2.35 |
What is the pKa of cysteine side chain?
The pKa values for the α-carboxylic acid and the α-amino acid groups is cysteine are 1.092 and 10.78, respectively. The pKa for the titratable −SH side chain in the amino acid is 8.33. Calculate the pI of cysteine. The structure of cysteine at pH = 7 shows that the side group is protonated.
Why does cysteine have a pKa?
The pKa of a cysteine represents the balance of the equilibrium thiol S–H % thiolate S− . Since thiolates are much more re- active than neutral thiols, they are critical to the function of many cysteines.
What is the pKa of amino group?
1.4. 1 Acid-base Chemistry of Amino Acids
| Amino acid | Functional Group | Side chain pKa |
|---|---|---|
| Glutamic acid | -COOH | 4.3 |
| Histidine | Imidazole ring | 6.0 |
| Arginine | Guanidino | 12.5 |
| Lysine | -NH2 | 10.5 |
What is the pKa for the amino acid cysteine?
The pKa values for the α-carboxylic acid and the α-amino acid groups is cysteine are 1.092 and 10.78, respectively. The pKa for the titratable −SH side chain in the amino acid is 8.33. Calculate the pI of cysteine. Solution The structure of cysteine at pH = 7 shows that the side group is protonated.
What is the structure of cysteine at pH 7?
Solution The structure of cysteine at pH = 7 shows that the side group is protonated. So we must conclude that even though the pKa is 8.33, the sulfhydryl (−SH) is acting as an acid. The isoelectric point, pI, is the pH at which the zwitterion is the dominant species.
Which is the best example of a pKa value?
pKa Data Compiled by R. Williams page-1 pKa Values INDEX Inorganic 2 Phenazine 24 Phosphates 3 Pyridine 25 Carboxylic acids 4, 8 Pyrazine 26 Aliphatic 4, 8 Aromatic 7, 8 Quinoline 27 Phenols 9 Quinazoline 27 Alcohols and oxygen acids 10, 11 Quinoxaline 27 Amino Acids 12 Special Nitrogen Compounds 28 Peptides 13 Hydroxylamines 28
What are the PKA and pI of arginine?
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 Glutamic acid Glu E 2.19 9.67 4.25 3.22 Glutamine Gln Q 2.17 9.13 – 5.65 Glycine Gly G 2.34 9.60 – 5.97 Histidine His H 1.82 9.17 6.00 7.59