The presence of food in the stomach leads to the secretion of pepsinogen by the chief cells of the gastric mucosa. The Fate of Amino Acids: Absorbed amino acids could be used for tissue protein, enzym...The presence of food in the stomach leads to the secretion of pepsinogen by the chief cells of the gastric mucosa. The Fate of Amino Acids: Absorbed amino acids could be used for tissue protein, enzyme, and hormone synthesis and deamination or transamination, and the carbon skeleton can be used for energy. Protein digestion in the ruminant animals can be divided into two phases: (1) digestion (degradation) in the reticulorumen and (2) digestion in the abomasum and small intestine.