1. What is Protein Net Charge?

The net charge of a protein is the sum of all positive and negative charges on its amino acid side chains and termini at a given pH. It's crucial for understanding protein solubility, stability, and interactions.

2. How Does the Calculator Work?

The calculator uses the net charge equation:

Where:

• Each amino acid contributes charge based on its pKa and the solution pH
• N-terminus and C-terminus also contribute to the net charge
• Charges are calculated using Henderson-Hasselbalch principles

Explanation: The calculator sums the charges of all ionizable groups in the protein at the specified pH.

3. Importance of Net Charge Calculation

Details: Knowing a protein's net charge helps predict its behavior in electrophoresis, ion exchange chromatography, solubility, and formulation stability.

4. Using the Calculator

Tips: Enter the protein sequence (single-letter codes) and the desired pH. The calculator will determine the net charge at that pH.

5. Frequently Asked Questions (FAQ)

Q1: Which amino acids contribute to net charge?
A: Aspartic acid (D), glutamic acid (E), lysine (K), arginine (R), histidine (H), and the N- and C-termini.

Q2: How does pH affect net charge?
A: As pH increases, acidic groups lose protons (become negative) and basic groups lose protons (become neutral).

Q3: What is the isoelectric point (pI)?
A: The pH at which the protein has zero net charge. This calculator helps estimate charge at any pH.

Q4: Are post-translational modifications considered?
A: This basic calculator doesn't account for PTMs. Specialized tools would be needed for phosphorylated or glycosylated proteins.

Q5: How accurate is this calculation?
A: It provides a theoretical estimate. Actual charge may vary due to protein folding and local environment effects.