Isoelectric Point Calculator

Isoelectric Point (pI, pH(I), IEP) is the pH value at which the particular molecule carries no net electrical charge or electrically neutral in statistical Mean. The concept is particularly important for zwitterionic molecules such as amino acids,peptides and proteins. The standard nomenclature to represent the isoelectric point is pH(I). Separation of proteins at the isoelectric point is called isoelectric focusing.

The formula for isoelectric point is Average sum of dissociation constant of an acid(pKa) and dissociation constant of base(pKb)

pI =(pKa +pKb)/2

• Where pI indicates the isoelectric point
• pka indicates the dissociation constant of acid
• pkb indicates the dissociation constant of base.

How to Calculate Isoelectric Point?

Procedure to calculate isoelectric point is as follows

• Enter the value of dissociation constant of an acid, it is indicated as pKa
• Enter the value of dissociation constant of a base, it is indicated as pKb
• Then click on the calculate button to get isoelectric point (pI).

Question 1:

What is pI (Iso electric point) of Tyrosine?

Solution:

Given that, dissociation constant of tyrosine are 2.2 and 9.11

pKa1 = 2.2

pKa2 = 9.11

Formula to find Isoelectric point pI = (pka1 +pka2)/2

Now substitute dissociation values in formula

pI = (2.2 +9.11)/2

pI = 5.66

Question 2:

Dissociation constant of acid is 5 and the dissociation constant of base is 4. Find the Isoelectric point of protein?

Solution:

Given that, Dissociation constant of acid = 5

Dissociation constant of base = 4

Formula to find iso electric point pI = (pka1 +pka2)/2

Now substitute values in formula = (5+4)/2

Isoelectric point of protein is 4.5

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• One important characteristic of monoclonal antibodies(mAbs) is their isoelectric point(pI), where essentially is the pH at which the antibody has no net electrical charge,and its value depends on the charged amino acids the antibody contains. If the pH of the surrounding environment is below the antibody’s pI, then the molecule carries a net positive charge,whereas the antibody will carry a net negative charge. When the pH is above the pI.
• Isoelectric point(pI) can play an important role in protein purification because it represents the pH where solubility is typically minimal.
• The isoelectric point (pI) concept is particularly important for zwitterionic molecules such as amino acids,peptides and proteins.
• Isoelectric point is an important characteristic for any amino acid,because every amino acid has at least two acid-base groups.
• The Isoelectric point of a protein will shift if the protein is combined with metal ions. Ex. isoelectric point of insulin is 5.3, but it increases to 6.2 when combined with Zn²⁺

1. What is meant by an isoelectric point?

The isoelectric point (pI) is defined as the pH at which no net migration takes place in an electric field.

2. What is the formula for isoelectric point?

The formula for isoelectric point is the average sum of dissociation constant of an acid(ka) and dissociation constant of base(kb). pI =(pKa +pKb)/2

3. What is the isoelectric point of milk?

The isoelectric point of casein is 4.6. Since milk’s pH is 6.6,casein has a negative charge in milk

4. What is the use of isoelectric point?

The isoelectric point is significant in protein purification because it represents the pH where solubility is typically minimal.

5. What are the differences between pI and pH?

pH is the measure of acidity. It is the negative logarithm of concentration of hydrogen ions present in the solution, pI known as isoelectric point, this is the pH at which a molecule has a net neutral charge.

6. What is meant by the isoelectric point of amino acids?

The isoelectric point of amino acid is the point at which the amino acid has no net electric charge.