[Leu15]-Gastrin I human (Amino Acid Sequence Glp-Gly-Pro-Trp-Leu-Glu-Glu-Glu-Glu-Glu-Ala-Tyr-Gly-Trp-Leu-Asp-Phe-NH2) encodes for the protein [Leu15]-Gastrin I in human. In human chromosome, the gene GAST is localized on 17q21.2. G cells in the stomach antrum produces the precursor of [Leu15]-Gastrin I, progastrin.Progastrin undergoes cleavage and processing to yield gastrin, which is trophic for the entire gastrointestinal epithelium. Gastrin is essential for the growth of the digestive system and stimulates the production of gastric acid by parietal cells. Gastrin exerts its function through G-protein-coupled receptor called the cholecystokinin (CCK) or CCK-B receptor (CCK-BR). Gastrin release is stimulated by food, especially protein diet and is inhibited by very low pH. Atrophic gastritis, a Helicobacter pylori infection and long-term administration of proton pump inhibitors infection may cause overexpression of gastrin. Gastric adenocarcinoma show high levels of gastrin.