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Query: UMLS:C0432222 (SEM)
 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Resealed erythrocyte ghosts have been used to define the kinetics of tracer exchange across the membrane-bound terminal complex of the complement cascade (C5b-9). Under steady-state conditions and at net chemical equilibrium, C5b-9 ghosts showed no significant lysis above control levels as measured by hemoglobin efflux. In 1 mM sucrose at 37 degrees C, [14C]sucrose isotopic exchange diffusion into C5b-9 ghosts occurred at 4.8 (+/- 0.5, SEM) X 10(-20) mol sec-1 per functional lesion, equivalent to an apparent permeability coefficient of 4.8 X 10(-14) cm3 sec-1 for the single C5b-9 lesion. No significant uptake of [14C]sucrose above control levels was observed in C5b67 ghosts. The apparent rate of tracer permeation through the complement lesion is one to two orders of magnitude slower than predicted by a model of a transmembrane channel of dimensions permitting free diffusion of sucrose. The data support earlier assertions from this laboratory that diffusion of small molecules across the complement lesion in biological membranes is significantly restricted.
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PMID:Steady-state analysis of tracer exchange across the C5b-9 complement lesion in a biological membrane. 28 15

The purpose of this study was to examine whether neutral endopeptidase and angiotensin I-converting enzyme, two membrane-bound metalloenzymes that are widely distributed in the microcirculation, play a role in bradykinin-induced increase in vascular permeability in the hamster cheek pouch. Changes in vascular permeability were quantified by counting the number of leaky sites and by calculating the clearance of fluorescein isothiocyanate (FITC)-dextran (molecular mass, 70,000 d) during suffusion of the cheek pouch with bradykinin. Bradykinin produced a concentration- and time-dependent increase in the number of leaky sites and clearance of FITC-dextran. The selective, active site-directed neutral endopeptidase inhibitors phosphoramidon (1.0 microM) and thiorphan (10.0 microM) and the selective angiotensin I-converting enzyme inhibitor captopril (10.0 microM) each shifted the concentration-response curve to bradykinin significantly to the left. During suffusion with bradykinin (1.0 microM) and phosphoramidon, the number of leaky sites increased significantly from 17 +/- 2 to 27 +/- 4 sites per 0.11 cm2 (mean +/- SEM, p less than 0.05), and FITC-dextran clearance increased significantly from 1.0 +/- 0.2 to 2.1 +/- 0.3 ml/sex x 10(-6).(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Role of peptidases in bradykinin-induced increase in vascular permeability in vivo. 131 17

The neuropeptide Y (NPY) receptor was solubilized from rat brain membranes with the zwitterionic detergent 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate (CHAPS). The binding of 125I-NPY to CHAPS extracts was protein, time, and temperature dependent. Unlabeled NPY and the related peptides peptide YY (PYY) and pancreatic polypeptide inhibited 125I-NPY binding to solubilized receptors with relative potencies similar to those seen with membrane-bound receptors: NPY greater than PYY much greater than pancreatic polypeptide. Scatchard analysis of equilibrium binding data showed the CHAPS extracts to contain a single population of binding sites with a KD of 3.6 +/- 0.4 nM (mean +/- SEM) and a Bmax of 5.0 +/- 0.2 pmol/mg of protein. In addition the 125I-NPY binding to the soluble receptor was not inhibited by guanosine-5'-O-(3-thiotriphosphate), in contrast to the GTP sensitivity displayed by the membrane-bound receptor. Gel filtration chromatography using Sepharose 6B revealed a single peak of binding activity corresponding to a Mr of approximately 67,000, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis after chemical cross-linking revealed a single band at Mr 62,000. After solubilization and gel chromatography a 50- to 100-fold purification of the NPY receptor was obtained.
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PMID:Solubilization of the neuropeptide Y receptor from rat brain membranes. 184 54

The present study was carried out to determine whether the major steroidogenic organelles of luteal cells quantitatively reflect variations in ovarian steroid secretion rates during pregnancy in the rat. Assessments were made on day 16 and in the morning (AM) and afternoon (PM) of day 22 (term is day 23). Ovarian steroidogenesis differs both quantitatively and qualitatively between these stages of pregnancy, so together they provide an ideal physiological model to study structural-functional relationships in the ovary. Corpora lutea of five rats were examined at each stage after progesterone and 20 alpha-hydroxypregn-4-en-3-one (20 alpha-OHP) secretion rates had been determined by a venous outflow technique. Total progestin secretion (progesterone plus 20 alpha-OHP) fell from 32.5 +/- 5.2 to 9.8 +/- 1.2 micrograms/hr per ovary (mean +/- SEM) between day 16 and day 22 AM but then increased to 22.6 +/- 1.4 micrograms/hr per ovary by day 22 PM. The total volume of luteal cell cytoplasm was slightly greater at day 22 AM and PM than at day 16. Similarly, the volumes of smooth endoplasmic reticulum (SER), lipid droplets, and membrane-bound granules all increased, but the volume of mitochondria decreased slightly. In contrast, the surface areas of SER and the inner and outer mitochondrial membranes did not change between day 16 and day 22 AM but then increased substantially by day 22 PM. Therefore, steroid secretion rates per unit area of steroidogenic membrane showed no consistent pattern over the stages examined.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Quantitative changes in steroidogenic organelles in the corpus luteum of the pregnant rat in relation to progestin secretion on day 16 and in the morning and afternoon of day 22. 204 55

Endopeptidase 24.11, a widely distributed membrane-bound peptidase is found in low levels in the serum of normal individuals. Although increased levels of the enzyme have been found in sera of patients with sarcoidosis and adult respiratory distress syndrome, the cellular origin of circulating endopeptidase 24.11 remains unknown. As the brush border of the proximal tubular epithelial cells have the highest endopeptidase specific activity, we investigated the possible contribution of the kidney to the release of endopeptidase 24.11 in the systemic circulation. Therefore, we measured serum levels of the enzyme in patients with end-stage renal failure (ESRF) treated by haemodialysis (HD) or continuous ambulatory peritoneal dialysis (CAPD). Increased serum levels of endopeptidase 24.11 were observed both in HD patients (mean +/- SEM: 74.6 +/- 20.9 ng/ml) and in CAPD patients (mean +/- SEM: 45.1 +/- 8.1 ng/ml) as compared to normal individuals (mean +/- SEM: 13.6 +/- 1.4 ng/ml). Endopeptidase levels remain stable during haemodialysis sessions on two different dialysis membranes. Finally, serum levels of the enzyme in anephric patients tend to be lower than in ESRF patients, suggesting that the kidney may contribute to the generation of the circulating form of endopeptidase 24.11.
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PMID:Increased serum levels of endopeptidase 24.11 ('enkephalinase') in patients with end-stage renal failure. 254 94

Studies of steroids and plasma lipoproteins in male cigarette smokers reveal that smoking is associated with an increase in peripheral estrogens and a decrease in high-density lipoprotein-cholesterol (HDL-C). We hypothesized that the lower HDL-C in this setting results in part from induction of the hepatic metabolic pathway that inactivates estrogen. This pathway, estradiol 2-hydroxylation, produces the peripherally inactive catechol estrogens 2-hydroxyesterone and 2-methoxyestrone. We used an in vivo radiometric method to assess 2-hydroxylation in 20 male smokers and 16 nonsmokers. The extent of the reaction (+/- SEM) was significantly higher among the smokers (43.3% +/- 1.9% v 24.6% +/- 1.9%, P less than .001). Smokers also excreted more urinary 2-hydroxyestrone (10.4 +/- 1.3 micrograms/g creatinine v 6.3 +/- 0.73 micrograms/g in nonsmokers, P = .011). The ratio of urinary 2-hydroxyestrone to estriol was higher on average among smokers (1.46 +/- 0.19 v 0.81 +/- 0.11, P = .006), and individual values correlated well with the radiometric test (r = .71, P less than .002). These data indicate that smoking is associated with significantly increased estrogen 2-hydroxylation in men. Preliminary evidence suggests that the smoking effect on C-2 hydroxylation may be opposed by ethanol. Elevated 2-hydroxylation in smokers, in the setting of modestly increased peripheral estrogens and a net decrease in HDLC, may be explained by the fact that lipoprotein synthesis and estrogen 2-hydroxylation both occur predominantly in the liver. Thus, greater metabolic inactivation of hepatic estrogens in male smokers could reduce HDLC, despite a modest rise in circulating hormone levels.
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PMID:Cigarette smoking alters hepatic estrogen metabolism in men: implications for atherosclerosis. 272 92

A semi-quantitative and semi-qualitative comparative analysis was performed on the maculae and cochleas of 3 patients. The cochleas were examined by SEM and the maculae by TEM and light microscopy. The surface features of the cochleas were minimally affected by autolysis. Hearing loss and increasing age correlated well with inner and outer hair cell counts. In the labyrinth, the sacculi were more resistant to autolysis than were the utriculi and the type 2 cells better preserved than the type 1 cells. The pattern of cellular degeneration in the utriculus and sacculus varied with both age and functional deficit. Lipofuscin was present in the sensory cell of all 3 patients but was most pronounced in the oldest. Long-spaced collagen, laminated bodies and membrane-bound inclusions were seen in all maculae.
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PMID:A comparative study of the effect of age on the human cochlear and vestibular neuroepithelia. 282 25

The origin and mechanism of the secretion of membrane-bound particles in bovine seminal plasma were studied with transmission (TEM) and scanning (SEM) electron microscopy of the epididymis, vas deferens, ampulla, and seminal vesicle of adult bulls. In the SEM study, all these organs were found to contain apical protrusions in the lining of the epithelial cells. Eventually the protrusions became detached and formed secretory bodies within the lumina of these organs. In the epididymis, the TEM study disclosed a granular and rather homogeneous content in the protrusions and bodies, whereas in the vas deferens they contained dilated cisternae of smooth endoplasmic reticulum. In the ampulla and seminal vesicle, the formation of the apical protrusions was associated with an accumulation of membrane-bound vesicles. These vesicles were found to be released from the storage bodies into the secretory fluid of the lumen. Both could be harvested from isolated seminal vesicle secretions by Percoll gradient centrifugation. It was concluded that various parts of the bovine reproductive organs discharge their secretory products at least partly by an apocrine mechanism. The membrane-bound particles in the seminal plasma, however, appear to be mainly derived from the ampulla and seminal vesicle.
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PMID:Electron microscopic study of the secretion process in bovine reproductive organs. 323 78

It has recently been recognized that human serum contains a protein that specifically binds human growth hormone (hGH). This protein has the same restricted specificity for hGH as the membrane-bound GH receptor. To determine whether the GH-binding protein is a derivative of, or otherwise related to, the GH receptor, we have examined the serum of three patients with Laron-type dwarfism, a condition in which GH refractoriness has been attributed to a defect in the GH receptor. The binding of 125I-labeled hGH incubated with serum has been measured after gel filtration of the serum through an Ultrogel AcA 44 minicolumn. Nonspecific binding was determined when 125I-hGH was incubated with serum in the presence of an excess of GH. Results are expressed as percent of specifically bound 125I-hGH and as specific binding relative to that of a reference serum after correction is made for endogenous GH. The mean +/- SEM of specific binding of sera from eight normal adults (26-46 years of age) was 21.6 +/- 0.45%, and the relative specific binding was 101.1 +/- 8.6%. Sera from 11 normal children had lower specific binding of 12.5 +/- 1.95% and relative specific binding of 56.6 +/- 9.1%. Sera from three children with Laron-type dwarfism lacked any demonstrable GH binding, whereas sera from 10 other children with other types of nonpituitary short stature had normal relative specific binding. We suggest that the serum GH-binding protein is a soluble derivative of the GH receptor. Measurement of the serum GH-binding protein may permit recognition of other abnormalities of the GH receptor.
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PMID:Absence of serum growth hormone binding protein in patients with growth hormone receptor deficiency (Laron dwarfism). 347 20

The properties of a cell surface nucleoside 5'-triphosphatase have been studied in small, intact, frog skeletal muscles, as a means of distinguishing the enzyme from other adenosine 5'-triphosphatases and of understanding its behaviour in the muscle membrane. The ectoenzyme in situ was shown to be a Ca2+- or Mg2+-activated ATPase liberating 7.5 +/- 0.4 (mean +/- SEM, n = 30) mumol of inorganic phosphate/g of muscle per 20 min, when the muscle was exposed to 2 mM ATP and 2 mM Ca2+ in Ringer's solution. The apparent Km for Mg2+ was 0.74 mM and for Ca2+ was 0.23 mM. A residual ATPase activity (20%) was found in the complete absence of divalent cations suggesting the existence of two ATPase types. A broad specificity toward nucleoside 5'-triphosphates was exhibited by the ecto-ATPase, but there was no nonspecific phosphatase activity. The enzyme was inhibited by La3+ and Cd2+, but was insensitive to ouabain, 2,4-dinitrophenol, oligomycin, and ruthenium red. Thus the ectoenzyme was not a Na+, K+-transport ATPase, was not an ATPase of mitochondrial origin, or a Ca2+-transport enzyme. Insulin had no effect. Inhibition by mersalyl, carbodiimide, and polar and cross-linking nonpolar nitrobenzene derivatives suggested that, for maximum activity, this membrane-bound enzyme required free sulfhydryl groups, certain free carboxyls, and an appreciable degree of hydrophobicity in its microenvironment.
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PMID:Characteristics of skeletal muscle ecto-ATPase in situ. 615 Jul 52


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