Concentrating hormones into secretory granules: layers of control

Soluble protein hormones are concentrated and stored in secretory granules The cisternal maturation model for transport of proteins through the Golgi complex allows a major role for formation of reversible aggregates as a mea ns of both concentrating and sorting hormones, since soluble proteins will be removed in small vesicles, leaving behind the aggregated hormones. The s torage of secretory granule proteins, however, is more selective than would be expected if passive aggregation were the only process involved. Aggrega tion of hormones in the secretory pathway may not be completely passive, bu t may be controlled by the cells. In addition to aggregation, other layers of sorting must exist, because there is selective retention of proteins aft er aggregation or packaging into granules. (C) 2001 Elsevier Science Irelan d Ltd. All rights reserved.