39. He then purified the peptide with the correct sequence from bacteria, but could not elicit the same response as endogenous peptides when he supplied it to culture neuronal cells. What is likely going wrong? (A) peptide is engulfed by autophagosome (B) peptide is degraded by Cas9-CRISPR (C) peptide is degraded by E3 ubiquitin ligases (D) lack of covalent bonds (E) lack of post-translational modification on the peptide