Isolation of renal membranes that contain kallikrein, angiotensin I-converting enzyme (kininase II) and angiotensinase in the rat

1. Fractions highly enriched in plasma membrane, endoplasmic reticulum or brush border were prepared from rat kidney cortex. Kallikrein was concentrated in the plasma membrane fraction, but not in the brush border fraction. Angiotensin I-converting enzyme (kininase II) and angiotensinase were localized in the brush border membrane. 2. It is suggested that kallikrein in the urine may originate from plasma membrane distal to the brush border of proximal tubules and the conversion of angiotensin I and the inactivation of bradykinin and angiotensin II may occur on the lumen membrane of the proximal tubular cells.

Isolation of membrane-bound renal enzymes that metabolize kinins and angiotensins

Cortex of rat kidney was homogenized and fractions enriched in plasma membrane, endoplasmic reticulum or brush border were prepared by several techniques of differential centrifugation. The identity and homogeneity of the membrane fragments were investigated by assaying marker enzymes and by transmission and scanning electron microscopy. Kallikrein was present in both plasma-membrane- and endoplasmic-reticulum-enriched fractions isolated by two fractionation procedures. Kallikrein was highly concentrated in a plasma-membrane fraction but was absent from the brush-border membrane of proximal tubular cells. Cells of transplanted renal tumours of the rat, originating from the proximal tubule, had no kallikrein activity. Kininase activity, angiotensin I-converting enzyme (kininase II) and angiotensinase were found in a plasma-membrane-enriched fraction and especially in the fraction containing isolated brush border. It is suggested that after renal kallikrein is synthesized on endoplasmic reticulum, it is subsequently reoriented to a surface membrane for activation and release. Renal kallikrein may enter the tubular filtrate distal to the proximal tubules. The brush-border membrane of proximal tubule is the major site of inactivation of kinins and angiotensin II..

Localization of angiotensin converting enzyme (kininase II). I. Preparation of antibody-hemeoctapeptide conjugates

Antibodies to pig lung angiotensin converting enzyme (kininase II) were conjugated to a heme-octapeptide (8-microperoxidase, 8-MP) derived from cytochrome c. 8-MP, which has only one reactive amine, was coupled to antibody in a two-step procedure using a bifunctional active ester, bis-succinyl succinate. In the first-step, 8-MP-succinyl succinate, a stable compound which can be stored. In a second step, the remaining active ester was used for coupling to reactive amines of the antibody. The conjugate consists of 1.6-2.3 8-MP moieties per antibody. Using these procedures, the formation of complex polymers is avoided. Each molecule of conjugate possesses both immunoreactivity and peroxidatic activity. The conjugate has been used to localize angiotensin converting enzyme along the plasma membrane and associated caveolae of pig aortic endothelial cells in culture.

Localization of angiotensin converting enzyme (kininase II). II. Immunocytochemistry and immunofluorescence

The cellular and subcellular sites of angiotensin converting enzyme (kininase II) in lung tissue and endothelial cells in culture were examined by immunocytochemical and immunofluorescence techniques. Converting enzyme is capable of inactivating bradykinin and of converting angiotensin I to its potent lower homolog, angiotensin II. Immunocytochemistry at the electron microscope level used goat anti- (pig lung and angiotensin converting enzyme) coupled to 11-MP (11-microperoxidase) via glutaraldehyde or to 8-MP (8-microperoxidase) via a bifunctional active ester, bis-succinyl succinate. The latter conjugate, which does not contain complex polymers, has been characterized in detail in terms of immunoreactivity and peroxidase activity.

[Properties and action specificity of carboxycathepsin (peptidyl dipepsidase) from bovine kidneys]

Carboxycathepsin from bovine kidney split the dipeptide fragments from the C-terminal part of peptides of different structure. Peptides containing the proline residue at the second position from the C-terminal amino acid residue and also peptides with substituted terminal alpha-carboxyl group were not hydrolyzed by carboxycathepsin. The enzyme was activated by Cl, Zn2+, Co2+ and Mn2+. The substances which formed the chelate complexes with ions of two-valent metals and also heavy metal ions, inhibited the enzymatic activity. Diisopropyl fluorophosphate did not inhibit carboxycathepsin. The homogeneous preparation of carboxycathepsin converted angiotensin 1 into angiotensin 11 and hydrolyzed bradikinine, splitting off C-terminal dipeptides consequentially.

A sensitive radiochemical assay for angiotensin-converting enzyme (kinase II)

[[125I]Tyr8]Bradykinin is degraded by angiotensin-converting enzyme to [125I]Tyr-Arg. The reaction product can be separated completely and recovered nearly quantitatively from unchanged substrate by cation-exchange chromatography. Thus it is possible to use [[125I]Tyr8]bradykinin at high specific radioactivity (about 400Ci/mmol) to measure the small quantities of angiotensin-converting enzyme encountered in small-scale cultures of pulmonary endothelial cells.

Angiotensin-I-converting enzyme activity in idiopathic respiratory distress syndrome of the newborn infant and in experimental alveolar hypoxia in mice

Serum angiotensin-I-converting enzyme activity was found to be elevated in infants with idiopathic respiratory distress syndrome when compared with healthy premature infants, normal infants, and acutely ill full-term infants. Serum and lung CE activity has been found to be elevated in mice exposed to hypobaric alveolar hypoxia which also stimulated renal renin production. These findings suggest that alveolar hypoxia stimulates the renin-angiotensin-aldosterone system and this system may be involved in the response to the stress of IRDS.

Subcellular localization of pulmonary antiotensin-converting enzyme (kininase II)

Goat antibodies to pig lung angiotensin-converting enzyme (kininase II) were conjugated to microperoxidase. Rat lung tissue, previously incubated with non-immune goat serum, was incubated with the antibody-microperoxidase conjugate and then with H2O2 and 3,3-diaminobenzidine. Electron microscopy revealed reaction product on the plasma membrane and caveolae of endothelial cells, especially those of capillaries and venules. These results support the hypothesis that angiotensin I and bradykinin are metabolized by enzymes on the luminal surface of pulmonary endothelial cells.

Mechanism of the pro-inflammatory activity of sympathomimetic amines in thermic oedema of the rat paw

1 Thermic oedema induced by heating rat paws at 46.5 degrees C was potentiated by local injection of adrenaline, noradrenaline or high doses of isoprenaline. The pro-inflammatory effect of sympathomimetic amines was antagonized by phenoxybenzamine or phentolamine but not by propranolol.2 The subcutaneous space of heated rat paws was perfused with Tyrode solution and the perfusate collected and assayed for bradykinin, bradykininogen, kinin-forming activity and kininase activity. When adrenaline (0.5 mug/ml) was included in the perfusion fluid, kininase activity of the perfusate was increased by 76% and free bradykinin reduced by 46%.3 Increased vascular permeability induced by injection of bradykinin or kallikrein was reduced by adrenaline or noradrenaline, but isoprenaline had no significant effect.4 Pretreatment with soya bean trypsin inhibitor (SBTI) or heparin did not antagonize the pro-inflammatory effect of adrenaline or thermic oedema per se.5 Potentiation of thermic oedema similar to that induced by sympathomimetic amines was obtained by injecting paws with vasopressin prior to heating, or by applying a ligature to stop blood flow to the paw for the first 15 min of heating.6 Thermistor probes inserted beneath the paw skin showed that sympathomimetic amines increased the internal temperature of heated paws. This was significant, as small changes in temperature had a marked effect on the development of thermic oedema.7 It is suggested that sympathomimetic amines potentiate thermic oedema of rat paws heated at 46.5 degrees C by reducing blood flow to the paw, thereby causing a greater rise in paw temperature and consequently greater injury.