Protein Hormone Storage in Secretory Granules: Mechanisms for Concentration and Sorting1

I. Introduction: Concentrating Protein Hormones in Secretory Granules II. A Well Characterized Sorting Mechanism: Lysosomal Hydrolases A. Sorting is linked to transport B. Specific transport is associated with specific vesicles III. Sorting of Soluble Transported Proteins in the Endoplasmic Reticulum A. Sorting in yeast B. Sorting in mammalian cells C. Implications for sorting into granules IV. Two Models for the Functioning of the Golgi Complex A. Vesicular transport of proteins vs. maturation of stacks B. Implications for sorting into granules V. Models for Formation of Secretory Granules A. Active budding off of secretory granules vs. active budding off of everything else B. Implications for sorting into granules VI. Hormone Aggregates in Cells A. Evidence for their existence B. Properties of hormone aggregates in cells VII. Hormone Aggregates in Solution VIII. Does Aggregation Cause Sorting in Cells? A. Ways to measure sorting B. Does sorting in cells correlate with aggregation in solution? IX. What Keeps Secretory Proteins from Aggregating? X. Sorting in the trans-Golgi Network A. Transmembrane proteins B. Soluble proteins XI. Sorting Signals and Sorting Signal Receptors for Secretory Granules XII. All Secretory Granule Proteins Are Not Treated Equally XIII. Summary.