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Angiotensin I

A decapeptide (ten-amino acid peptide) angiotensin produced by cleaving angiotensinogen by renin, and is involved in no known direct biological activity but as a precursor to angiotensin II (the active form of angiotensin)
Angiotensin is an oligopeptide hormone involved in the regulation of blood pressure. In particular, it causes vasoconstriction, which leads to an increase in blood pressure. It comes from angiotensinogen (an alpha-2-globulin) chiefly from the liver. The angiotensinogen is a 60 kd polypeptide produced and released mainly from the liver. Angiotensin level increases due to the activity of corticosteroid, estrogen, thyroid hormone, and angiotensin II.
Angiotensinogen in the plasma is converted into angiotensin I. This is through the action of renin. The renin cleaves the peptide bond between leucine and valine residues of angiotensinogen. This leads to the formation of the decapeptide, angiotensin I.
The angiotensin I is biologically inactive. It has to be cleaved again to become angiotensin II, which is the biologically active form of angiotensin. The enzyme that catalyzes the turning of angiotensin I to angiotensin II is called angiotensin-converting enzyme (ACE). The angiotensin II is the form that causes the contraction of vascular smooth muscle, which in turn, raises the blood pressure as well as stimulates the release of aldosterone from the adrenal glands.
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