Which one of the following is not a digestive enzyme in the human system?

Gastrin is not a digestive enzyme but a peptide hormone secreted by gastric G cells that stimulates gastric acid secretion and thereby regulates digestion; it is released into the bloodstream to act on parietal and enterochromaffin-like cells rather than directly catalysing food breakdown [1]. In contrast, ptyalin (salivary amylase) is an active enzyme in saliva that begins starch digestion in the mouth [2]; trypsin is a pancreatic protease that digests proteins in the small intestine [3]; and pepsin is the stomach protease that breaks down proteins in an acidic environment [4]. Therefore gastrin functions as a regulatory hormone, not as a digestive enzyme.

Sources

1. [1] https://www.ncbi.nlm.nih.gov/books/NBK534822/
2. [2] https://www.ncbi.nlm.nih.gov/books/NBK544242/
3. [3] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Activity 5.3 > p. 86
4. [4] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Activity 5.3 > p. 85