Answer:
Stomach
Pepsin
Step-by-step explanation:
Protein first digested chemically in the stomach. The peptic or chief cells of the gastric glands secrete the proenzyme pepsinogen. The proenzyme pepsinogen gets activated by the hydrochloric acid. In the presence of hydrochloric acid (HCL), it is activated into the pepsin, an active enzyme. Pepsin is functional only in the in acidic medium. In the stomach the medium is acidic, thus pepsin converts proteins into proteoses and peptones (peptides).