angiotensin i Angiotensin I: A decapeptide that is cleaved from precursor angiotensinogen by RENIN. Angiotensin I has limited biological activity. It is converted to angiotensin II, a potent vasoconstrictor, after the removal of two amino acids at the C-terminal by ANGIOTENSIN CONVERTING ENZYME.. angiotensin I : A ten amino acid peptide formed by renin cleavage of angiotensinogen. Angiotensin I has no direct biological function except that high levels can stimulate catecholamine production. It is metabolized to its biologically active byproduct angiotensin II, a potent vasoconstrictor, by angiotensin converting enzyme (ACE) through cleavage of the two terminal amino acids.. angiotensin I dizwitterion : A peptide zwitterion that is the dizwitterionic form of angiotensin I having both carboxy groups deprotonated and the aspartyl amino group and arginine side-chain protonated. It is the major species at pH 7.3. | 1.97 | 1 | 0 | angiotensin; peptide zwitterion | human metabolite; neurotransmitter agent |