what is the charge on each of the followin amino acid at physiologic pH:
glutamate
lysine
valine
tyrosine
histidine
To determine the charge on each amino acid at physiologic pH, we need to consider the pKa values of their functional groups and the pH at which the measurements are made.
First, let's look at the pKa values of the amino acid side chains:
1. Glutamate (Glu): Glutamate has a carboxyl group (COOH) as its side chain. The pKa value for this group is around 4.1. At pH values below its pKa, the carboxyl group will be protonated (charged), while at pH above its pKa, it will be deprotonated (uncharged).
2. Lysine (Lys): Lysine has an amino group (NH2) as its side chain. The pKa value for this group is around 10.5. Similar to glutamate, at pH values below its pKa, the amino group will be protonated (charged), while at pH above its pKa, it will be deprotonated (uncharged).
3. Valine (Val): Valine does not have any ionizable groups in its side chain. Therefore, it will remain uncharged at all pH values.
4. Tyrosine (Tyr): Tyrosine contains both a phenolic group (OH) and an aromatic amino group (NH2) in its side chain. The pKa value for the phenolic group is around 10.1, while the pKa value for the amino group is around 9.6. At pH values below their respective pKa values, both groups will be protonated (charged). At pH values between their pKa values, the phenolic group will be deprotonated while the amino group will remain protonated. At pH values above their pKa values, both groups will be deprotonated (uncharged).
5. Histidine (His): Histidine has an imidazole group (NH-C3H3N2) as its side chain. The pKa value for the imidazole group is around 6.0. At pH values below its pKa, the imidazole group will be protonated (charged), while at pH values above its pKa, it will be deprotonated (uncharged).
To calculate the charge at physiologic pH, you need to know the specific pH range considered physiologic. Typically, physiologic pH is around 7.4. Based on the pKa values mentioned above, you can determine the protonation state of each amino acid at this pH.
- At pH 7.4:
- Glutamate will be deprotonated (charged -1).
- Lysine will be protonated (charged +1).
- Valine will be uncharged.
- Tyrosine will be deprotonated (uncharged).
- Histidine will be a mixture of protonated and deprotonated forms (charged +1/+0).
Remember that these charges are approximate and can vary depending on the specific experimental conditions.