Figure 1. Progastrin processing.

A, schematic of the main products of preprogastrin processing. The signal sequence (green) of preprogastrin is cleaved in the endoplasmic reticulum and progastrin then passes through the Golgi complex to secretory vesicles where it is cleaved (dashed arrows) and the COOH-terminus amidated; processing enzymes are indicated in the boxes. B, the pathways of post-translational processing of rat preprogastrin as revealed by pulse-chase kinetic studies are shown together with a summary of the main biological properties of the various progastrin-derived peptides. C, putative mechanisms regulating progastrin processing are shown: selected cleavages are inhibited by raising intravesicular pH and by phosphorylation by physiological casein kinase. The inset shows the primary sequence of the cleavage/phosphorylation site in the single-letter notation. Cleavage sites (Arg^57,58, Lys^74,75, Arg^94,95) are also identified in the single-letter notation.