Plasma angiotensinases

Three enzymes hydrolyzing angiotensin have been described in normal human plasma. Angiotensinase A₁ is an aminopeptidase requiring Ca⁺⁺ and a pH optimum of 7.4. It specifically hydrolyzes asparagine¹-angiotensin. Angiotensinase A₂ is also an aminopeptidase, requiring Ca⁺⁺ and has a pH optimum of 6.8. It specifically hydrolyzes aspartic acid¹-angiotensin. Angiotensinase B is an endopeptidase, requiring no cofactor with a pH optimum of 5.8 – 6.0. It hydrolyzes all angiotensin analogs studied and is inhibited by diisopropylfluorophosphate.Plasma angiotensinase activity usually measures angiotensinase A₁ since it is conducted at pH 7.4 with asparagine¹-angiotensin as substrate. In 133 hypertensive patients and 42 normal controls, no significant differences were found in the level of angiotensinase A₁ activity. Occasionally patients will be found whose plasma enzymes destroy angiotensin at increased rates possibly due to increase in nonspecific proteolytic enzymes.