[Clinical study on the angiotensin I-converting enzyme in human urine. (I) Partial purification, enzymic characteristics and excretion in normal subjects].

The angiotensin I-converting enzyme in normal human urine was partially purified with ammonium surfate (3.2M), DEAE-Cellulose ion exchange chromatography (0-0.5M NaCl gradient), and Sephadex G 200 gel filtration. The enzyme was separated into three forms which had different molecular weights of 700000, 290000 and 40000, respectively. The enzymic biochemical characteristics of these three enzymes, however, were identical with regard to their inhibitory effects (bradykinin potentiator c, arg-pro-pro, o-phenanthroline and EDTA), Cl- dependency, optimal pH (8.3) and temperature (37 degrees C), and Km value (2.3mM). The enzymic activity was determined in five normal subjects in three conditions of dietary sodium intake (51, 153 and 340mEq for 5 days, respectively). The enzymic activity correlated well with the concentration of the excreted sodium (r = 0.87, p less than 0.001). There was no significant relation between the enzymic excretion and the concentration of the excreted potassium, nor between the activity and the creatinine excretion. It is suggested that the origin of urinary angiotensin I-converting enzyme is the kidney, and that the enzyme might regulate sodium excretion in cooperation with renal kallikrein-kinin system.