Kininase II-type enzymes: their putative role in muscle energy metabolism

Bradykinin and kallidin ([Lys.sup.1]-bradykinin) have a variety of actions besides affecting blood pressure; these actions have been the subject of many investigations through the years. For example, kinins antagonize smooth [...]
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 [P.sub.3] fraction of the heart and skeletal muscles, angiotensin I-converting enzyme (ACE) and neutral endopeptidase 24.11 (NEP) are the major kininases, as determined first with specific substrates and second with bradykinin. ACE activity was highest in guinea pig heart (2.7 ± 0.07 μmol [multiplied by] [h.sup.-1 [multiplied by] mg [protein.sup.-1]) 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 [multiplied by] [h.sup.-1 [multiplied by] mg [protein.sup.-1] in cultured neonatal cardiac myocytes and varying between 0.12 and 0.05 μmol [multiplied by] [h.sup.-1 [multiplied by] mg [protein.sup.-1] in human, dog, rat, and guinea pig heart. In the skeletal muscle [P.sub.3], ACE was most active in guinea pig and rat (1.2 and 1.1 μmol [multiplied by] [h.sup.-1 [multiplied by] mg [protein.sup.-1], respectively) but less so in dog (0.09 μmol [multiplied by] [h.sup.-1 [multiplied by] mg [protein.sup.-1]). NEP activity was higher in dog [P.sub.3] (0.28 μmol [multiplied by] [h.sup.-1 [multiplied by] mg [protein.sup.-1]) but lower in rat and guinea pig (0.19 and 0.1 μmol [multiplied by] [h.sup.-1 [multiplied by] mg [protein.sup.-1], respectively). Continuous density gradient centrifugation enriched NEP activity in dog and rat (from 0.3 to 1.0 and 0.49 μmol [multiplied by] [h.sup.-1 [multiplied by] mg [protein.sup.-1], respectively). Immunoprecipitation with antiserum to purified NEP proved the specificity of the rat enzyme. Bradykinin (0.1 mmol/l) 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/l), 46 and 55% of kininase in rat and dog skeletal muscle [P.sub.3], respectively, was due to ACE; 36 and 28%, respectively, was due to NEP. Aside from these enzymes, an aminopeptidase in Mt [P.sub.3] 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