Structural changes of Amino Acids according pH values

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Structural changes of Amino Acids according pH value

 

 

Hello friends , welcome back to my blog … today I will discuss about how you can easily determine the structural changes along different pH value . Lets make it easy….

Amino acid

pKa1

 pKa2

pKa3

   pI

Glycine

2.34

 9.60

  ---

  5.97

Alanine

2.34

 9.69

  ---

  6.00

Valine

2.32

 9.62

  ---

  5.96

Leucine

2.36

 9.60

  ---

  5.98

Isoleucine

2.36

 9.60

  ---

  6.02

Methionine

2.28

 9.21

  ---

  5.74

Proline

1.99

10.60

  ---

  6.30

Phenylalanine

1.83

 9.13

  ---

  5.48

Tryptophan

2.83

 9.39

  ---

  5.89

Asparagine

2.02

 8.80

  ---

  5.41

Glutamine

2.17

 9.13

  ---

  5.65

Serine

2.21

 9.15

  ---

  5.68

Threonine

2.09

 9.10

  ---

  5.60

Tyrosine

2.20

 9.11

  ---

  5.66

Cysteine

1.96

 8.18

  ---

  5.07

Aspartic acid

1.88

 9.60

  3.65

  2.77

Glutamic acid

2.19

 9.67

  4.25

  3.22

Lysine

2.18

 8.95

10.53

  9.74

Arginine

2.17

 9.04

12.48

10.76

Histidine

1.82

 9.17

  6.00

  7.59

Table of pKa and pI values

  • The pKa values and the isoelectronic point, pI, are given below for the 20 α-amino acids.
  • pKa1= α-carboxyl group, pKa2 = α-ammonium ion, and pKa3 = side chain group.

Lets discus about the rule for determining the structure for amino acids

1.      if the pH < pka then protonation [as there will more H+ present for protonation of amino acids because of less pH]

2.      if the pH > pka then deprotonation [ as the pH is high then there will more OH- ready to grab H+ to make H2O]

 

lets take an example ….lysine   at pH =1,9 and 5

 



 

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