1. What is Isoelectric Point?

The isoelectric point (pI) is the pH at which a molecule carries no net electrical charge. For amino acids, it's calculated as the average of the two pKa values that bracket the neutral form.

2. How Does the Calculator Work?

The calculator uses the pI equation:

Where:

• \( pKa1 \) — First acid dissociation constant
• \( pKa2 \) — Second acid dissociation constant

Explanation: The equation averages the two pKa values that correspond to the neutral form of the amino acid.

3. Importance of pI Calculation

Details: The pI is crucial for understanding protein behavior in electrophoresis, solubility, and purification techniques like isoelectric focusing.

4. Using the Calculator

Tips: Enter both pKa values (must be positive numbers). The calculator will compute the average as the pI.

5. Frequently Asked Questions (FAQ)

Q1: How is pI different for proteins vs amino acids?
A: For proteins, pI is calculated using all ionizable groups (not just two pKa values) and can be more complex to determine.

Q2: What are typical pI values for amino acids?
A: Most amino acids have pI values between 5.0-6.5, except for basic (e.g., lysine ~9.7) and acidic (e.g., aspartate ~2.8) ones.

Q3: Why is pI important in biochemistry?
A: pI helps predict protein solubility (least soluble at pI) and is used in separation techniques like isoelectric focusing.

Q4: How does pH relate to pI?
A: At pH < pI, molecules are positively charged; at pH > pI, they're negatively charged; at pH = pI, net charge is zero.

Q5: Can this calculator be used for proteins?
A: No, this simple formula is only for amino acids. Protein pI calculation requires considering all ionizable groups.