Insulin Is a Secretory Protein Made by the β Cells

Insulin is a secretory protein made by the β cells in the pancreas. This protein …

A) is released by the β cells in response to increased intracellular Ca²⁺ concentration.
B) is first synthesized as preproinsulin.
C) is stored as aggregates inside secretory vesicles in the β cells.
D) undergoes proteolytic cleavage before secretion.
E) All of the above.