# 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