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Query: EC:3.1.3.1 (alkaline phosphatase)
 47,916 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Rat placental cells (RPCs) derived from the chorioallantoic placenta of day-12 Holtzman rats were tested for the expression of class I and class II RT I histocompatibility antigens, transferrin receptors, intermediate filaments, and alkaline phosphatase. The binding of mouse monoclonal antibodies to those antigens by RPCs was compared with the binding of the same reagents to rat placental cells in situ. RPCs expressed low levels of class I antigens and failed to express detectable levels of class II antigens. RPCs resisted up-regulation of expression of class I antigens by interferon-gamma, and did not express class II antigens following exposure to medium containing interferon. Transferrin receptors; cytokeratin intermediate filaments, and alkaline phosphatase were universally expressed by RPCs. Taken together with the patterns of expression of the same antigens by rat placental cells in situ, the results suggest that RPCs comprise labyrinthine trophoblast cells. Those cells may provide a valuable new approach for studying the structures and functions of trophoblast cells in vitro.
Placenta
PMID:Expression of histocompatibility antigens, transferrin receptors, intermediate filaments, and alkaline phosphatase by in vitro cultured rat placental cells and rat placental cells in situ. 313 46

The dynamics of the release of human placental lactogen (hPL) under basal conditions and response to various secretogogues has been studied in perifused enriched hPL-producing cells from term placentae prepared by the isopycnic centrifugation of collagenase/hyaluronidase-dispersed placental cells on Percoll gradients. Under basal conditions, the perifused cells released hPL at a relatively constant rate for up to 24 h in culture. The mean rates of hPL release from cells (5 x 10(6) cells) from 18 normal full-term placentae varied from 1.8 to 20.2 ng/5 min (mean 7.7 ng/5 min). The cells from term placentae, however, did not release detectable amounts of chorionic gonadotrophin or the cytosolic enzymes lactic dehydrogenase and alkaline phosphatase. The amounts of hPL released by the perifused cells were inversely related to cell density with mean rates of hPL release by 2, 5, and 10 x 10(6) cells of 15.8, 8.6, and 5.7 ng/10(6) cells/0.5 h. The perifused cells responded to provocative stimuli (high-density lipoproteins (HDL), apolipoproteins AI, AII, and CI, partially purified hPL-releasing factor, phorbol esters, sn-1,2-diacylglycerol, and cAMP) in a manner qualitatively similar to enriched trophoblast cells and placental explants in static culture. Release of hPL in response to HDL, apoproteins AI, AII, and CI, and partially purified hPL-releasing factor was dose-dependent and occurred within 5 min of exposure. Basal and stimulated hPL release by perifused trophoblast cells that had been previously frozen at -70 degrees C for four weeks was identical to that of freshly dispersed cells from the same placenta. These experiments indicate that perifused trophoblast cells may be used as a model system to examine the dynamics of hPL release under basal conditions and in response to provocative stimuli.
Placenta
PMID:Characterization of placental lactogen release from perifused human trophoblast cells. 339 89

Proteins of the basal and microvillous plasma membranes of the human placental syncytiotrophoblast were compared to elucidate the basis for structural and functional differences in the two membranes. Among the proteins common to both membranes were actin, alkaline phosphatase, albumin, transferrin, immunoglobulin G, proteins of Mr 35,000, 55,000 and 180,000, and five immunochemically detected proteins. Each membrane also contained unique proteins. Major microvillous cytoskeleton proteins of Mr 68,000 80,000 and 105,000 (alpha-actinin) were lacking or absent from basal membrane cytoskeletons which instead contained unique proteins of Mr 14,000, 16,000, 220,000 and 240,000. In addition, immunochemical analyses revealed four glycoprotein antigens unique to microvillous membrane and five unique to basal membrane. Fibronectin was also found to be exclusive to basal membrane. The difference in membrane-associated cytoskeletal proteins correlated with the different organization of actin microfilaments at the two membranes. The protein antigens unique to each of the two membranes provided further evidence for the polarization of membrane proteins and functions in the syncytium.
Placenta
PMID:Proteins of the apical and basal plasma membranes of the human placental syncytiotrophoblast: immunochemical and electrophoretic studies. 343 56

Placental-type alkaline phosphatase (PLAP) has been purified from human term syncytiotrophoblast microvillous plasma membranes by immunoaffinity chromatography using the immobilized monoclonal antibodies H317 and H315. The eluted enzymatically active PLAP had a molecular weight in the regions of 115K and 130K, with an occasional higher molecular weight form at 180K. On reduction to a 66K monomeric form, both enzymatic activity and immunoactivity against the PLAP-reactive monoclonal antibodies were lost. The monomeric form of syncytiotrophoblast microvillous plasma membrane- (StMPM-)associated PLAP displayed electrophoretic polymorphism on 2D-PAGE.
Placenta
PMID:Isolation of placental-type alkaline phosphatase associated with human syncytiotrophoblast membranes using monoclonal antibodies. 378 93

Human placental microvillous alkaline phosphatase (M-PLAP) was extracted from microvilli either by butanol extraction or subtilisin proteolysis. The data indicate that subtilisin cleavage of PLAP removes a membrane-binding domain of approximately 2000 molecular weight, leaving the catalytic site intact and the protein in solution. Sequencing studies on the N-terminal 13 amino acids of both the subtilisin-cleaved and uncleaved forms of M-PLAP indicate that the enzyme is anchored to the plasma membranes by its carboxy-terminus. The N-terminal 13 amino acids of A-PLAP were the same as those of M-PLAP. Trypsin solubilization failed to release M-PLAP from these membranes and it appears to cleave a portion of molecular weight of about 9K from the amino terminus, leaving an enzymatically active portion of PLAP associated with the membrane. On SDS gels, subtilisin-cleaved M-PLAP showed an apparent dimeric molecular size larger than that of the original uncleaved enzyme, presumably due to the generation of a less compact conformational state. On starch gels, cleaved M-PLAP showed a single zone of enzyme activity with a mobility sightly greater than that of A-PLAP, which did not require the presence of Triton X-100 to enter the gel. Variations in the apparent molecular sizes of the different allelic forms of PLAP were also observed.
Placenta
PMID:Placental alkaline phosphatase integrates via its carboxy-terminus into the microvillous membrane: its allotypes differ in conformation. 390 24

A simple procedure is described for the further purification of placental microvillus preparations. Based on previously published methods for the isolation of microvilli from other tissues, it depends on the preferential aggregation of containing structures by Mg2+. In the purified microvillus preparation, the two placental microvillar marker enzymes, alkaline phosphatase and 5'-nucleotidase, were enriched 24-fold and were obtained in 5 per cent yield. Five other microvilla enzymes were also further enriched by the Mg2+-treatment. Marker enzymes for other subcellular components showed that this treatment completely removed contamination by mitochondria and endoplasmic reticulum and contamination by lysosomes was decreased three-fold. (Na+ + K+)-activated ATPase was depleted by the Mg2+-treatment as was beta2-microglobulin.
Placenta
PMID:An improved method for the preparation of human placental syncytiotrophoblast microvilli. 625 28

Subcellular fractionation of human term placenta showed that the highest relative specific activity of 5'-nucleotidase and alkaline phosphatase resided in the microsomal fraction; of the total 5'-nucleotidase activity present, 7 per cent was in the cytosol. 5'-Nucleotidase was reproducibly purified over 500-fold in 17 per cent yield from the insoluble component of homogenates of term placenta to give a single major glycoprotein with two minor inactive protein contaminants. Purified placental 5'-nucleotidase was free from non-specific or alkaline phosphatase, hydrolysed 12 to 22 mumol AMP/min/mg of protein at 30 degrees C, and was activated up to fivefold by Triton X-100. AMP, Km 5 to 7 microM, was the preferred substrate. The Arrhenius plot was biphasic, with activation energies of 21.7 and 49.7 kJ/mol above and below 36 degrees C, the region of the transition temperature. Nucleoside di- and triphosphates inhibited competitively; the most potent inhibitors were ADP and adenosine 5'-methylenediphosphonate, Ki slope 90 nm and 6 nm, respectively. Lectins inhibited the enzyme; concanavalin A caused time-dependent inactivation reversible by alpha-methyl-D-mannoside. EDTA inactivated the enzyme; partial reactivation was achieved with divalent cations. The pH optimum was 7.2 to 7.3; Mg2+ produced a second alkaline pH optimum. The properties of placental 5'-nucleotidase are those of an intrinsic membrane protein and, in general, resemble properties of the several 'ecto'-5'-nucleotidases which have been purified from other tissues, although certain differences in kinetic properties of the placental enzyme are apparent.
Placenta
PMID:Human placental 5'-nucleotidase: purification and properties. 632 73

A simple method for the purification of human placental nuclei is described. Nuclei were isolated by homogenizing tissue in standard saline citrate solution in the presence of zinc chloride to stabilize the nuclear membranes, NP40 as non-ionic detergent and sodium bisulphite for inhibition of proteolytic activity. Nuclei purification was achieved by low-speed centrifugation through a discontinuous sucrose gradient. The purified nuclei were evaluated by morphological criteria using phase contrast and electron microscopy. The extent of contamination by cytoplasmic debris was estimated by Papanicolaou's staining technique. Biochemical criteria include measurements of alkaline phosphatase activity as a plasma membrane enzyme marker and DNA-dependent RNA polymerase activity for the functional integrity of nuclear components. Transcriptionally active nuclei were obtained but the yield of nuclei was low; however, this low yield is compensated by the high degree of purity, the simplicity of the method and the functional and morphological integrity of the purified nuclei.
Placenta
PMID:Low-speed purification of human placental nuclei. 652 84

Microvillous membrane fractions from human term placentae were prepared by differential centrifugation. Extration of membranes with PBS-EDTA or KCI removed soluble cytoplasmic components and serum proteins excepting trace amounts of albumin and transferrin. PAGE-SDS revealed 11 components in the Triton solubilized crude fraction after PBS-EDTA extraction. Membrane components solubilized with Triton were not fractionated by gel filtration on Bio-Gel A-50 m but DEAE-cellulose chromatography partially resolved these components. Three fractions were obtained by stepwise elution of absorbed materials using increasing concentrations of NaCl in the equilibrating buffer. These fractions were characterized using SDS-PAGE. The material unabsorbed to the DEAE contained two components of small molecular weight and one of them showed a positive PAS stain. The first eluted protein peak showed nine components, seven of which stained with PAS. The bulk of glycoproteins with molecular weights greater than 130 000 daltons were found in this fraction. The second eluted peak from DEAE was rich in components with molecular weights less than 42 000 daltons. Four components in this fraction were not identified in the other two ion-exchange fractions. Bands representing mobilities of albumin, transferrin and alkaline phosphatase were observed in DEAE-cellulose fractions; however, 12 components of unknown structure were revealed.
Placenta
PMID:Characterization of solubilized microvillous membrane proteins and glycoproteins from human placental syncytiotrophoblast. 723 34

At the electronoptical level the placental villi of the pre-eclamptic woman are characterized by focal syncytial necrosis, loss and distortion of microvilli, dilatation of syncytial rough endoplasmic reticulum, decreased syncytial pinocytotic activity, a reduced number of syncytial secretory droplets, cytotrophoblastic hyperplasia, degeneration of occasional cytotrophoblastic cells, thickening of the trophoblastic basement membrane and the presence of small fetal capillaries with bulbous endothelial cells. Ultrahistochemical studies show reduced alkaline phosphatase and dehydrogenase activity in the syncytiotrophoblast but an increased acid phosphatase activity. It is suggested that all the observed morphological abnormalities, with the exception of cytotrophoblast cell degeneration, are explicable solely on the basis of utero-placental ischaemia and that no other aetiological factor need be invoked: the cause of the cytotrophoblast cell degeneration is, however, unknown. The ultrastructural findings indicate that there is a decrease in the transfer and synthetic activity of the trophoblast and that cellular respiration is also probably depressed. Nevertheless, there is some evidence that changes of a compensatory nature, designed to limit the effects of the tissue damage, are brought into play.
Placenta
PMID:An ultrastructural and ultrahistochemical study of the human placenta in maternal pre-eclampsia. 744 36


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