PRESENCE OF ANGIOTENSIN-CONVERTING ENZYME (ACE) ACTIVITY IN SERUM OF AMPHIBIAN - COMPARISON WITH ACE ACTIVITY OF MAMMALIAN SERUM

The occurrence of angiotensin converting enzyme (EC 3.4.15.1; ACE) was demonstrated for the first time in serum of newt (Triturus carnifex) and frog (Rana esculenta). The enzymatic activity was evidenced follow ing hydrolysis of N-[3-(2-furyl) acryloyl]L-phenylalanyl glycyl glycin e (FAPGG), a synthetic substrate of ACE. The serum enzyme liberated N- [3-(2-furyl) acryloyl]L-phenylalanine (FAP) from FAPGG, The properties of the amphibian serum enzymes were compared with those of swine. The amphibian serum FAPGG hydrolysing activities were inhibited by typica l ACE inhibitors, captopril and lisinopril. The optimum of pH was 8.3 at 10 and 37 degrees C and the temperature optimum was 45 degrees C. T he values were similar to those of swine serum. The FAPGG Michaelis-Me nten constants (Km) at 37 degrees C of amphibian serum enzymes (0.337 mM and 0.282 mM for frog and newt, respectively) were lower than that of swine (1.305 mM), but close to human serum enzyme. The Km values ob tained at 10 degrees C were lower than those at 37 degrees C (0.152, 0 .086, and 1.029 mM for frog, newt, and swine serum, respectively). Amp hibian sera hydrolysed bullfrog synthetic angiotensin I to produce ang iotensin II. Captopril (50 mu M) inhibited the production of angiotens in II.