Figure 11.

The renin-angiotensin and kallikrein-kinin systems. In both systems, a substrate is cleaved by an enzyme of restricted specificity, releasing a peptide that is either already active (lysbradykinin, bradykinin) or inactive (angiotensin I). Upon further processing by a specific peptidase, angiotensin I is converted to a vasoactive peptide (angiotensin II). In turn, vasoactive peptides are inactivated by peptidases. Angiotensin-Converting enzyme is common to both systems but has different roles: it processes angiotensin I to angiotensin II and is the main kinin-inactivating peptidase. [Reprinted from Liu et al. (143).]