New suggestions for the physiological role of secretory protein-I.

A major endocrine secretory protein of unknown function termed secretory protein-I or, alternatively, chromogranin A, is attracting increasing attention. Because of its abundance and apparently universal presence in endocrine and neuroendocrine cells, many suggestions for a physiological role have been advanced. Recent data provide the first firm bases for some proposed functions that include a regulator of a novel protease capable of converting prohormones to hormones, a hormone precursor, and through its calcium-binding and aggregating properties, a secretory granule condensing protein.