🤓 Based on our data, we think this question is relevant for Professor Ratliff's class at USF.
What is the charge of the tetrapeptide Lys-Lys-His-Glu at pH 7?
The charge of proteins and polypeptides would depend on the condition of the dissociable protons along the chain. These include the protons in the C terminal, the N terminal, and the side chains.
The protons in the C terminal and in the acidic side chains dissociate at pH lower than 7. This leaves a negative charge from each of those substituents. Meanwhile, the protons in the N terminal and those of the basic side chains dissociate at pH above 7. As long as these protons are attached to those basic groups, they will have a + charge per substituent.