PROPERTIES OF 3 DIFFERENT FORMS OF ANGIOTENSIN I-CONVERTING ENZYME FROM HUMAN LUNG

We compared some properties of three different forms of angiotensin I-converting enzyme from human lung obtained with trypsin treatment. The inhibition studies were performed using bradykinin potentiator C, Arg-Pro-Pro and EDTA. The I50 values for these inhibitors on the enzymes of peak I (mol. wt. 290 000) and peak II (mol. wt. 180 000) were identical (bradykinin potentiator C, 5 · 10-6 M; Arg-Pro-Pro, 1.2 · 10-4 M; EDTA, 5 · 10-5 M). But the enzymic activity of peak III (mol. wt. 98 000) was not inhibited by bradykinin potentiator C and Arg-Pro-Pro. the I50 value for EDTA on the enzyme of peak III was 2 · 10-3 M. The enzymic activities of peak I and peak II were reduced to 10% of the initial level of the enzymic activity by the preincubation for 10 min at 50°C, but the enzymic activity of peak III to 55%. The pH optimums for three different forms of the enzyme were identical and pH 8.3 in potassium phosphate buffer, but the pH optimums were changed and pH 7.3-8.0 in borate/sodium carbonate buffer. Km values of three different forms of the enzyme for Hippuryl-His-Leu-OH were identical and 0.6 mM in borate/sodium carbonate buffer, pH 7.8. The enzymic activities of peak I and peak II were dependent of Cl- ion, but the enzymic activity of peak III was independent of Cl- ion. Moreover, the enzymes of peak I and peak II were adsorbed on a column of concanavalin A-Sepharose, but the enzyme of peak III was not adsorbed on the column. It was suggested that the enzymes of peak I and peak II were glycoprotein, but the enzyme of peak III did not have a mannose in a suitable position to react with concanavalin A. © 1978.