Exopeptidases in human platelets: an indication for proteolytic modulation of biologically active peptides

The determination in human platelets of four exopeptidases--aminopeptidase P, dipeptidyl peptidase IV, carboxypeptidase N, and angiotensin converting enzyme--by means of fluorometric or liquid chromatography techniques was carried out. The results obtained show that the specific activities of dipeptidyl peptidase IV, carboxypeptidase N, and angiotensin converting enzyme in intact and disrupted platelets are small compared to their specific activities in serum. However, for aminopeptidase P the specific activity of this enzyme is much higher in platelets than in serum. This suggests that circulating platelets may have a significant role as scavengers for circulating peptides containing bonds susceptible for aminopeptidase P.

Distribution of angiotensin converting enzyme in human tissues

Angiotensin converting enzyme (EC 3.4.15.1, dipeptidyl carboxypeptidase, ACE, Kininase II), the peptidase which transforms inactive decapeptide, angiotensin I, to the pressor octapeptide, angiotensin II, and which catalyses also the degradation of vasodilative nonapeptide bradykinin, was measured in 27 human tissue homogenates and physiological fluids. Two assays were used: one which measures the hydrolysis of the substrate hippuryl-glycyl-glycine, by means of high performance liquid chromatography and another, using a colorimetric assay measuring the cleaved glycyl-glycine after arylation with picrylsulfonic acid. All the tissues studied contained measurable converting enzyme activities which were inhibited by captopril (SQ 14.225) in low concentrations. High specific activities of converting enzyme were found in several tissues of the intestinal and urogenital tract, but the highest activity was found in benign prostatic hyperplasia. Normal prostate and prostatic adenocarcinoma have a much lower activity. Results obtained for human tissues are compared with those found in animals.

Sensitive colorimetric assay for angiotensin converting enzyme in serum

A sensitive colorimetric procedure has been developed for the assay of angiotensin converting enzyme (EC 3.4.15.1) in serum. Serum (10 microL) is incubated for 30 min with hippuryl-glycyl-glycine as described earlier (Clin Chem 28: 1352-1355, 1982). After a Folin-Wu deproteinization, the liberated glycyl-glycine is derivatized with a borate-buffered (pH 9.3) trinitrobenzenesulfonate solution (60 mmol/L) to form trinitrophenyl-glycylglycine, the absorbance of which is read at 420 nm vs a serum blank. The linear range extends to an activity of more than 900 U/L of serum and the detection limit is less than 4 U/L. The mean activity for serum from 50 blood bank donors and 25 patients with active sarcoidosis was 281 (SD 77) and 693 (SD 81) U/L, respectively. The method demonstrates good precision (CVs less than 2.8%) and correlates well (r = .99) with results from a "high-pressure" liquid chromatographic procedure for determining hippuric acid. In addition, the proposed method is widely applicable, involving only commonly available apparatus.

Sensitive colorimetric assay for angiotensin converting enzyme in serum

A sensitive colorimetric procedure has been developed for the assay of angiotensin converting enzyme (EC 3.4.15.1) in serum. Serum (10 microL) is incubated for 30 min with hippuryl-glycyl-glycine as described earlier (Clin Chem 28: 1352-1355, 1982). After a Folin-Wu deproteinization, the liberated glycyl-glycine is derivatized with a borate-buffered (pH 9.3) trinitrobenzenesulfonate solution (60 mmol/L) to form trinitrophenyl-glycylglycine, the absorbance of which is read at 420 nm vs a serum blank. The linear range extends to an activity of more than 900 U/L of serum and the detection limit is less than 4 U/L. The mean activity for serum from 50 blood bank donors and 25 patients with active sarcoidosis was 281 (SD 77) and 693 (SD 81) U/L, respectively. The method demonstrates good precision (CVs less than 2.8%) and correlates well (r = .99) with results from a "high-pressure" liquid chromatographic procedure for determining hippuric acid. In addition, the proposed method is widely applicable, involving only commonly available apparatus.

Improved micromethod for assay of serum angiotensin converting enzyme

We describe conditions for determining angiotensin converting enzyme (EC 3.4.15.1) in serum, by liquid chromatography. Serum (10 microL) is assayed with the artificial substrate hippuryl-glycyl-glycine (30 mmol/L) in a 50 mmol/L "HEPES" buffer solution with a high salt content (300 mmol of NaCl and 400 mmol of Na2SO4 per liter), at pH 8.0. The resulting enzymic activity is ninefold that of the currently popular spectrophotometric assay of Cushman and Cheung as modified by Lieberman (Am. J. Med. 59: 365-372, 1975). The hippuric acid end product is separated from the substrate by reversed-phase liquid chromatography and measured spectrophotometrically at 228 nm. o-Methyl hippuric acid is used as internal standard. The mean value for 100 normal control subjects was 317 (SD 96) nmol of hippuric acid released per milliliter of serum per minute. The enzyme activity is greater in newborns (p less than 0.05) and has a tendency to decrease with age. This partly automated method, which is optimized with regard to activity and detection, can be used in clinical routine.

Improved micromethod for assay of serum angiotensin converting enzyme

We describe conditions for determining angiotensin converting enzyme (EC 3.4.15.1) in serum, by liquid chromatography. Serum (10 microL) is assayed with the artificial substrate hippuryl-glycyl-glycine (30 mmol/L) in a 50 mmol/L "HEPES" buffer solution with a high salt content (300 mmol of NaCl and 400 mmol of Na2SO4 per liter), at pH 8.0. The resulting enzymic activity is ninefold that of the currently popular spectrophotometric assay of Cushman and Cheung as modified by Lieberman (Am. J. Med. 59: 365-372, 1975). The hippuric acid end product is separated from the substrate by reversed-phase liquid chromatography and measured spectrophotometrically at 228 nm. o-Methyl hippuric acid is used as internal standard. The mean value for 100 normal control subjects was 317 (SD 96) nmol of hippuric acid released per milliliter of serum per minute. The enzyme activity is greater in newborns (p less than 0.05) and has a tendency to decrease with age. This partly automated method, which is optimized with regard to activity and detection, can be used in clinical routine.