Increased urinary excretion of angiotensin converting enzyme in patients with renal diseases

We measured the activity of angiotensin converting enzyme (ED 3.4.15.1) in urine samples from normal subjects and patients with nephrotic syndrome and chronic glomerulonephritis. Urinary excretion of angiotensin converting enzyme in patients with nephrotic syndrome (1.58 +/- 0.50 (SD) units/day; n = 15) and chronic glomerulonephritis (1.01 +/- 0.45 units/day; n = 12) was significantly increased compared with normal subjects (0.38 +/- 0.10 units/day; n = 18). It was demonstrated that a high molecular weight form of the enzyme (more than 400000) was mainly excreted in urines from patients with nephrotic syndrome. After trypsin treatment, this form was altered to a low molecular weight form (290000). These two different forms of urinary angiotensin converting enzyme were compared with the enzyme purified from human kidney, and found to be identical with respect to Km values (2 mmol/l), pH optimum (pH 8.3), chloride ion dependency (0.8 mol/l), inhibitory effect of captopril (I50, 21 nmol/l), and behavior towards antiserum to human kidney angiotensin converting enzyme.