The first mature form of an enzyme, before it develops into an active enzyme.
The inactive form in which certain enzymes (e.g. digestive enzymes) are originally produced and secreted. The existence of this inactive form prevents the enzyme from breaking down the cells in which it was made. Once the proenzyme has been secreted it is converted to the active form.
The inactive form of an enzyme found within a cell, which, upon leaving the cell, is converted into the active form, such as pepsinogen, which is cleaved to pepsin by hydrochloric acid in gastric juice.