Human plasma converting enzyme

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Angiotensin-converting enzyme was partially purified from human plasma by ammonium sulfate and Sephadex gel nitration. Some of its kinetic and physiological properties were discussed in comparison with those of hog plasma-converting enzyme. The K m value for human plasma converting enzyme was obtained as 4.5 × 10 −5 m. The S 20,W value (8.2) for the enzyme was obtained by the sucrose density gradient sedimentation technique and the same molecular weight for the converting enzyme in human and hog plasma was estimated to be about 150,000 daltons. The maximum activity of the enzyme in human plasma is about 4.5 units per ml, and the calculated half-time for the conversion of angiotensin I to angiotensin II is about 7 min. This slow rate, as in hog plasma, suggests that there must be more to the “activation” of angiotensin than is immediately obvious.