Two different processing pathways probably exist in antral G-cells. In the dominant pathway progastrin is cleaved at three sites resulting in two major bioactive gastrins, gastrin-34 and gastrin-17. In the putative alternative pathway, progastrin may be processed only at the most C-terminal dibasic site resulting in the synthesis of gastrin-71.
Sulfation enhances proteolytic processing, and blocks peptide degradation. Levels of sulfation differ between proteolytically-cleaved gastrins. Thus, gastrin-6 is almost 73% sulfated, whereas the larger gastrins are less than 50% sulfated. Sulfation levels are also tissue-specific.