In the stomach
Cells in the stomach wall produce hydrochloric acid and inactive forms of two enzymes, pepsinogen and prorennin. The liquid in which these enzymes and acid is found is known as gastric juice. The acid denatures much of the proteins found in the chicken patty of the burger so that they unravel and expose the polypeptides. It also converts the inactive forms of the enzymes to the active forms and provides a suitable pH for their action. Pepsin, for, pepsinogen, begins the hydrolysis of polypeptides into shorter chains.