Which protein-digesting enzyme secreted in the stomach - is not activated until it comes into contact with hydrochloric acid. sodium bicarbonate mucin protease pepsin

The answer is **pepsin**.<br /><br />Pepsin is secreted in its inactive form, pepsinogen, by the chief cells in the stomach lining. The hydrochloric acid (HCl), also produced in the stomach, provides the acidic environment necessary to convert pepsinogen into its active form, pepsin. This prevents the pepsin from digesting the proteins within the cells that produce it.<br />