Identification of two new calcium dependent hydrolases in the human heart.

We have identified and isolated two new calcium-activated neutral hydrolases from human ventricular muscles. The one is an esterase, of which molecular weight was 300,000, required millimolar concentration of Ca2+, hydrolyzed Ac-Tyr-OEt X H2O, optiaml pH at 7.0. The other is an amidase, of which molecular weight was 70,000, also required millimolar concentration of Ca2+, hydrolyzed a synthetic substrate for chymotrypsin, Suc-Leu-Leu-Val-Tyr-MCA, with optimal pH at 7.2. Both enzymes did not degrade casein or contractile proteins (myosin, actin, troponin and tropomyosin). Their activities were not inhibited by exogenous protease inhibitors, leupeptin, antipain, monoiodoacetic acid and chymostatin, while the amidase activity was blocked by the endogenous inhibitor against calcium-activated neutral protease (CANP). Thus, their characters are different from chymotrypsin or CANP and they seems to be new hydrolases in the human heart.