Figure 2.

The general fate of vitamin K–dependent proteins at the site of production. A: Under normal conditions. B: Under vitamin K depletion. 1: Preproprotein is synthesized from mRNA by ribosomes. 2: Preproprotein is targeted to the endoplasmic reticulum (ER), where the ER signaling sequence is removed and the protein is processed by (vitamin K–dependent) γ-glutamyl carboxylase. 3: Proprotein is carboxylated when vitamin K is present. 4: Carboxylated or 4a: uncarboxylated proprotein is transported to the Golgi apparatus, where the PRO-sequence is mostly cleaved (some proteins are also glycosylated there, not shown). 4b: In some cases under vitamin K deficiency, the uncarboxylated protein is cleft by proteasome. 5: Mature protein is extruded via a secretory vesicle into the extracellular space