angiotensin I

noun

-ˈwən 

: the physiologically inactive form of angiotensin that is composed of 10 amino acid residues, is derived from angiotensinogen, and is converted by angiotensin converting enzyme to angiotensin II

Angiotensin I is a decapeptide without apparent physiologic effect. In a single passage through the pulmonary circulation, angiotensin I is cleaved by a membrane-bound converting enzyme to produce angiotensin II, a very potent vasoconstrictor.

—Scientific American Medicine