INTRACELLULAR-TRANSPORT, SORTING, AND PROTEOLYTIC PROCESSING OF REGULATED SECRETORY PROTEINS DOES NOT REQUIRE PROTEIN SULFATION

The biological significance of protein sulfation is poorly understood. To study a possible role of protein sulfation in the regulated secret ory pathway, neurointermediate lobes (NIL) of the pituitary of South-A frican clawed toads (Xenopus laevis) were treated with chlorate, a pot ent in vivo inhibitor of protein sulfation. We monitored the fates of newly synthesized proopiomelanocortin (POMC), prohormone convertase (P C2), and secretogranin III (SgIII), which are sulfated and regulated s ecretory proteins. Inhibition of protein sulfation had no effect on th e proteolytic processing of these precursor proteins and the kinetics of release of their cleavage products. The release was sensitive to ap omorphine, a drug that blocks the release of proteins via the regulate d secretory pathway, indicating that no missorting to the constitutive pathway had occurred. Our results suggest that protein sulfation is n ot required for the intracellular transport, sorting, and proteolytic processing of regulated secretory proteins. (C) 1997 Elsevier Science Ireland Ltd.