Angiotensin I-converting enzyme from guinea pig lung and serum. A comparison of some kinetic and inhibition properties.

The angiotensin I-coverting enzyme (peptidyldipeptide hydrolase, EC 3.4.15.1) was isolated from both guinea pig lung and serum; Km and V values were determined using both angiotensin I and hippurylhistidylleucine as substrates. Km values for the lung enzyme were 3.1 mM for hippurylhistidylleucine hippurylhistidylleucine and 0.076 mM for angiotensin I. Inhibition studies were performed and I50 values were obtained with the following inhibitors: angiotensin II (lung, 1.9 - 10(-5) M; serum, 1.7 - 10(-5) M), bradykinin (lung, 2.6 - 10(-6) M; serum, 2.1 - 10(-6) M), and pyrrolidone-Lys-Trp-Ala-Pro (lung, 7.9 - 10(-8) M; serum, 5.6 - 10(-8) M). Both enzymes were glycoproteins and were inhibited by concanavalin A. A maximum inhibition of 35% initial enzymatic activity was observed for both enzymes at a concanavalin A concentration of 4 - 10(-4) M suggesting that the sugar moieties of each enzyme are similar. Both enzymes required NaCl for activity and were inhibited by EDTA. A comparison of kinetic and inhibition properties indicates that both enzymes are quite similar.