[A method for determining the angiotensin-converting enzyme activity in the rat hypothalamus and hypophysis]

A method for determination of the activity of angiotensin-converting enzyme (ACE) in the hypothalamus and hypophysis of the rat was provided. Membrane-bound enzyme was extracted from tissues by twice homogenization and centrifugation after solubilization of membrane structures with the detergent triton X-100. Protein concentrations of tissue extracts and time of incubation, at which there was linear generation of dipeptid his-lev in the course of the enzymic reaction as at the same time its degradation from tissue peptidases was under 10%, were between 0.16 and 0.35 mg/ml for the hypothalamus and between 0.07 and 0.18 mg/ml for the hypophysis with duration of incubation between 15 and 30 min. Under these conditions the enzymic activity was determined by a substrate-fal-his-lev, amounting to 18.22%-1.3 and 96.22-42 nmol/min/mg of protein (x-SEM) for the hypothalamus (n = 18) and hypophysis (n = 30) respectively. The coefficients of variation of the enzymic analysis were determined for a series in a day (1.37%) and for a series in time (9.59%). Hydrolyzing activity synonymously identified as ACE was differentiated from other tissue peptidildipeptide hydrolases by the following three criteria: hydrolyzing activity in respect to the specific for ACE artificial substrates; activation of enzymic action by Cl-; inhibition of the activity by converting inhibitors captopryl and MK 422 as well as by the helatic agent EDTA-Na2.