Aspartic acid, an amino acid, has the structure shown below. Which of the following best explains which proton is most acidic?

◦ Proton V is most acidic due to the possibility of conjugate base stabilization by resonance with the adjacent C=O bond.
◦ Proton I is most acidic due to conjugate base stabilization by resonance and being further from the inductive effect of the positive nitrogen atom.
◦ Proton II is most acidic due being attached to the carbon closest to the positive nitrogen atom.
◦ Proton IV is most acidic due to conjugate base stabilization by resonance and being closer to the inductive effect of the positive nitrogen atom.
◦ Proton III is most acidic due to being attached to a positive nitrogen atom.