What conversion does angiotensin I undergo to become angiotensin II?

Angiotensin I is converted to angiotensin II primarily by the action of angiotensin-converting enzyme (ACE). This enzymatic conversion takes place predominantly in the lungs, where ACE facilitates the removal of two amino acids from angiotensin I to produce angiotensin II, which is the more biologically active form involved in the regulation of blood pressure and fluid balance.

Angiotensin II plays several critical roles, including vasoconstriction, stimulating the release of aldosterone, and promoting the retention of sodium and water, ultimately increasing blood pressure. The importance of ACE in this conversion underscores its role as a therapeutic target in various cardiovascular and renal diseases, particularly with ACE inhibitors used to manage hypertension and heart failure.

While renin initiates the process of forming angiotensin I from angiotensinogen, it is ACE that completes the conversion to angiotensin II. The vascular endothelium does not directly transform angiotensin I into angiotensin II; rather, it is where the ACE enzyme is predominantly active. Aldosterone, primarily involved in sodium retention and blood pressure regulation, is a product of angiotensin II but does not play a role in the conversion process itself.