The enzyme that begins protein digestion in the stomach is called pepsin.
Pepsin is formed from its inactive precursor, pepsinogen, which is secreted by the gastric chief cells in the stomach lining. When food enters the stomach, the acidic environment (due to hydrochloric acid) activates pepsinogen into pepsin.
Pepsin plays a crucial role in protein digestion by breaking down the complex protein molecules into smaller peptides, making it easier for other enzymes in the small intestine to further digest these peptides into amino acids. This process is vital for our body to absorb the nutrients from the food we consume.