Ponto isoelétrico
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
(pKa1 + pKa2)/2
About this calculator
The Isoelectric Point (pI) is the pH at which a protein or amino acid has no net electric charge, balancing its protonated and deprotonated forms. For diprotic amino acids, this calculator uses the formula (pKa1 + pKa2)/2, where pKa1 and pKa2 correspond to the dissociation constants of the carboxylic and amino groups, respectively. This calculation is critical in biochemistry to predict molecular behavior in techniques like electrophoresis and chromatography.
This tool is primarily used in protein and amino acid studies. For instance, it helps determine protein solubility at different pH levels, vital for purification processes. However, for amino acids with more than two ionizable groups (e.g., arginine or cysteine), the pI calculation involves additional pKa values and specific methods, which are not covered by this simplified version.
When using the calculator, it is crucial to ensure accurate pKa values, which vary depending on the molecule and experimental conditions. Additionally, the (pKa1 + pKa2)/2 model applies only to diprotic amino acids. For more complex cases, such as proteins with multiple chains or post-translational modifications, advanced computational analysis is recommended.
Frequently asked questions
How is the isoelectric point calculated for diprotic amino acids?
For diprotic amino acids, the isoelectric point is calculated by summing the two pKa values (pKa1 and pKa2) and dividing by 2, using the formula (pKa1 + pKa2)/2.
Why is the isoelectric point important in protein purification?
The pI predicts the pH at which a protein has minimal solubility, aiding in techniques like electrophoresis and chromatography for separation and purification.
Can this calculator be used for all amino acids?
No, this tool applies only to diprotic amino acids. Amino acids with more than two ionizable groups require different methods.
What if an amino acid has more than two pKa values?
Amino acids with three or more ionizable groups (e.g., cysteine or histidine) require more complex calculations involving the relevant pKa averages, which are not included in this model.