DIABETES, VOLUME 45, SUPPLEMENT 1, JANUARY 1996, PAGES S34-S37

Kininase II-Type Enzymes
Their Putative Role in Muscle Energy Metabolism

Tomislav Dragovic, Richard Minshall, Herbert L. Jackman, Li-Xiu Wang, and Ervin G. Erdos

Because of the importance of bradykinin in improving heart function in some conditions or in enhancing glucose uptake by skeletal muscle, we investigated kininases in these tissues. In P3 fraction of the heart and skeletal muscles, angiotensin I-converting enzyme (ACE) and neutral endopeptidase 24.11 (NEP) are the mayor kininases, as determined first with specific substrates and second with bradykinin. ACE activity was highest in guinea pig heart (2.7 + 0.07 µmol · h^{-1 ·} mg protein^-l) but decreased in other species in this order: dog atrium, rat heart, dog ventricle, and human atrium. The specific activity of NEP was lower: 0.45 µmol^.h^{-1 ·} mg protein^-1 in cultured neonatal cardiac myocytes and varying between 0.12 and 0.05 ^µmol^.h^-1.mg protein^-1 in human, dog, rat, and guinea pig heart. In the skeletal muscle P₃, ACE was most active in guinea pig and rat (1.2 and 1.1 µmol. h^-1. mg protein^-l, respectively) but less so in dog (0.09 µmol ^· h^{-1 ·} mg protein^-l). NEP activity was higher in dog P₃ (0.28 µmol^. h^-1. mg protein^-l) but lower in rat and guinea pig (0.19 and 0.1 µmol^. h^-l. mg protein^-l, respectively). Continuous density gradient centrifugation enriched NEP activity in dog and rat (from 0.3 to 1.0 and 0.49 µmol^.h^-1.mg protein^-l, respectively). Immunoprecipitation with antiserum to purified NEP proved the specificity of the rat enzyme. Bradykinin (0.1 mmol/1) was inactivated in the presence and absence of inhibitors by rat skeletal muscle NEP, as measured by high-performance liquid chromatography. Here, 36% of the activity was caused by NEP and 19% by ACE. In radioimmunoassay (bradykinin 10 nmol/1), 46 and 55% of kininase in rat and dog skeletal muscle P₃, respectively, was due to ACE; 36 and 28%, respectively, was due to NEP. Aside from these enzymes, an aminopeptidase in rat P₃ also inactivates bradykinin. Thus, in conclusion, heart and skeletal muscle membranes contain kininase II-type enzymes, but their activity depends on the species. Diabetes 45 (Suppl. 1):S34-S37,1996

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