Enter the numbers of Arginine, Aspartic acid, Lysine, and Histidine residues into the calculator to determine the net charge of the protein. This calculator can also evaluate any of the variables given the others are known.

Protein Charge Formula

The following formula is used to calculate the net charge of a protein. Variables: 

Q = (nR - nD + nK + nH) * 1.602 x 10^{-19} C
  • Q is the net charge of the protein
  • nR, nD, nK, and nH are the numbers of Arginine, Aspartic acid, Lysine, and Histidine residues in the protein, respectively
  • 1.602 x 10^-19 C is the elementary charge, which is the absolute value of the charge of one proton

To calculate the net charge of a protein, count the number of Arginine, Aspartic acid, Lysine, and Histidine residues in the protein. Subtract the number of Aspartic acid residues from the number of Arginine residues, then add the number of Lysine and Histidine residues. Multiply the result by the elementary charge to get the net charge of the protein.

What is a Protein Charge?

A protein charge, also known as a net charge, refers to the overall electrical charge of a protein molecule. This charge is determined by the sum of the charges of the amino acids that make up the protein. Each amino acid has a specific charge, either positive, negative, or neutral, depending on its pH level. The protein’s charge can influence its structure, function, and interactions with other molecules. It’s also crucial in processes such as protein separation and purification.

How to Calculate Protein Charge?

The following steps outline how to calculate the Protein Charge using the given formula:

  1. First, determine the number of Arginine residues (nR) in the protein.
  2. Next, determine the number of Aspartic acid residues (nD) in the protein.
  3. Next, determine the number of Lysine residues (nK) in the protein.
  4. Next, determine the number of Histidine residues (nH) in the protein.
  5. After gathering all the necessary variables, use the formula Q = (nR – nD + nK + nH) * 1.602 x 10^-19 C to calculate the net charge of the protein (Q).
  6. Finally, calculate the Protein Charge by inserting the values of the variables and calculating the result.

Example Problem:

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

nR (number of Arginine residues) = 5

nD (number of Aspartic acid residues) = 3

nK (number of Lysine residues) = 2

nH (number of Histidine residues) = 1

1.602 x 10^-19 C (elementary charge) = 1.602 x 10^-19 C