how do I determine the total charge of Asn-Tyr-Asp with a pH 7.4
To determine the total charge of an amino acid sequence such as Asn-Tyr-Asp at pH 7.4, you need to know the pKa values of the ionizable groups within the amino acids.
1. Identify ionizable groups: In Asn-Tyr-Asp, there are three potentially ionizable groups: the carboxyl group (-COOH) in Asp, the amino group (-NH3+) in Asn, and the tyrosine side chain with a phenolic group (-OH) that can be ionized.
2. Determine the pKa values: The pKa values determine at which pH a specific ionizable group will be mostly ionized or mostly in its non-ionized form. For Asp, the pKa of the carboxyl group is around 2.1, for Asn the pKa of the amino group is around 8.7, and for tyrosine, the pKa of the phenolic group is around 10.1.
3. Calculate the charges at pH 7.4: At pH 7.4, you need to determine if each group will be charged or not.
- Asp: At pH 7.4, the carboxyl group of Asp is deprotonated and carries a negative charge (-COO-).
- Asn: At pH 7.4, the amino group of Asn is protonated and carries a positive charge (+NH3+).
- Tyrosine: At pH 7.4, the phenolic group of tyrosine is deprotonated and carries a negative charge (-O-).
4. Calculate the total charge: To calculate the total charge, simply add up the charges. In this case, Asp has -1 charge, Asn has +1 charge, and the tyrosine residue has -1 charge.
Therefore, the total charge of Asn-Tyr-Asp at pH 7.4 is -1 + 1 - 1 = -1.