Enter the dissociation constant of the acidic group and the dissociation constant of the basic group into the calculator to determine the isoelectric point. This calculator can also evaluate any of the variables given the others are known.

## Isoelectric Point Formula

The following formula is used to calculate the isoelectric point (pI) of a peptide.

pI = (pKa1 + pKa2) / 2

Variables:

- pI is the isoelectric point pKa1 is the dissociation constant of the acidic group pKa2 is the dissociation constant of the basic group

To calculate the isoelectric point, add the dissociation constant of the acidic group to the dissociation constant of the basic group. Then, divide the sum by 2.

## What is an Isoelectric Point?

The isoelectric point, often abbreviated as pI, is the pH at which a particular molecule or surface carries no net electrical charge. This concept is often applied to proteins, which can have both positive and negative charges on their amino acids. At the isoelectric point, the total number of positive and negative charges on the protein are equal, making the overall charge zero. This point is important in various applications, such as protein separation and purification.

## How to Calculate Isoelectric Point?

The following steps outline how to calculate the Isoelectric Point using the given formula:

- First, determine the values of pKa1 and pKa2.
- Next, add the values of pKa1 and pKa2 together.
- Then, divide the sum by 2.
- Finally, calculate the Isoelectric Point (pI).
- After inserting the values and calculating the result, check your answer with the calculator above.

**Example Problem:**

Use the following variables as an example problem to test your knowledge:

pKa1 = 4.5

pKa2 = 9.2