Angiotensin-1-Converting Enzyme (ACE) Activity in Human Serum following Plasma Exchange

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Abstract
Although angiotensin-1-converting enzyme (ACE) (which catalyzes both the conversion of angiotensin 1 to angiotensin 2 and the hydrolysis of bradykinin) is present in serum, little information is available about its source or turnover characteristics. The removal and recovery characteristics of serum ACE were determined for 2 normal subjects and 16 patients with various diseases who were undergoing partial plasma exchange. Cholesterol was removed as predicted, but the average actual removal of ACE, 70% of that originally present, was 28% greater than predicted. Recovery of serum levels of ACE after plasma exchange was 34% on Day 1, 62% on Day 3, 94% on Day 5 and 104% on Day 8, and the level remained relatively constant thereafter up to 28 days of study. The pattern of recovery of serum ACE is more compatible with a system of synthesis and release of ACE than with a simple exchange mechanism from sites on the plasma membrane of the endothelial cell or a shift of the enzyme from one space to another.