| Mammalian prosomatostatin (PSS) is cleaved at an Arg-Lys doublet in order to produce somatostatin-14 (SS-14), and at two singlets, Arg and Lys, in order to release SS-28 and PSS;Conclusions. (i) PSS is capable of monobasic processing within the constitutive secretory pathway. (ii) Such cleavages may be effected by furin or related endoproteases but are relatively inefficient. (iii) PC1 is capable of dibasic cleavage of PSS to SS-14 in both constitutive or regulated secretory cells. (iv) PC2 mediates SS-14 conversion only if expressed in regulated secretory cells. (v) The milieu of secretory cells, and not the granules, is required for PC2 activity. (vi) Furin is a mammalian SS-28 convertase, but not the unique one. (vii) A yet unknown endoprotease is responsible for PSS... |
