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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Purified microvillous membranes prepared from normal term human placenta were studied for their ability to bind specifically low-density lipoprotein (LDL). Electron microscopic examination of the membrane preparations revealed essentially microvilli-like structures, and the enzyme analyses a 14-17-fold enrichment in the membrane markers 5'-nucleotidase and alkaline phosphatase. The binding of [125I]LDL was dependent on time, temperature, pH and protein concentration; it was saturable with a low capacity (130.4 +/- 22.2 ng/mg of membrane protein) and presented a high affinity (apparent Ka 6.12 +/- 1.32 micrograms protein per ml). These high-affinity binding sites were specific for LDL (high-density lipoprotein induced less competition than unlabelled LDL) and were sensitive to pronase digestion. Unlike the binding of LDL to other tissues, the [125I]LDL binding to microvillous membranes did not require divalent cations. The presence of specific LDL receptors on the placental microvillous membranes, located at the effective site of exchange between the maternal blood and the placental tissue, supports the concept that human placenta utilizes LDL-cholesterol for its progesterone synthesis.
Mol Cell Endocrinol
PMID:Characterization of specific low-density lipoprotein binding sites in human term placental microvillous membranes. 629 42

A surface membrane fraction isolated from Leishmania donovani promastigotes contained distinct 5'- and 3'-nucleotidase activities. These were distinguished from each other, and from a previously described surface membrane nonspecific acid phosphomonoesterase, on the basis of several properties. The 5'- and 3'-nucleotidases had p' optima of 6.5 and 8.5, respectively. In contrast to the 3'-nucleotidase, the 5'-nucleotidase was inhibited by both ammonium molybdate and fluoride ions; the latter inducing a biphasic response. Neither divalent cations nor chelators affected the 5'-enzyme activity whereas the 3'-enzyme was inactivated by EDTA. This inactivation was fully reversed following removal of the chelator, either by resuspension of the membranes in EDTA free medium or by addition of certain divalent cations in excess; Co2+ being the most effective. The 5'-nucleotidase had activity with both ribo- and deoxyribonucleotide substrates, whereas the 3'-nucleotidase did not hydrolyse deoxyribonucleotides.
Mol Biochem Parasitol 1983 Apr
PMID:Evidence for distinct 5'- and 3'-nucleotidase activities in the surface membrane fraction of Leishmania donovani promastigotes. 630 42

Distinct 3'- and 5'-nucleotidase activities were localized to the surface membrane of Leishmania donovani promastigotes using enzymatic reactions with live intact cells and fine structure enzyme-mediated cytochemical reactions with intact cells, cell homogenates, and isolated surface membranes. The results indicated that virtually all activity of both enzymes was restricted to the parasite surface membrane. Cytochemical localization results demonstrated that both activities were externally disposed on the intact organism, and were restricted to the external face of the isolated parasite surface membrane. The two activities were cytochemically differentiated by their substrate specificities and sensitivity to several inhibitors. On the basis of their cytochemical sensitivity to glutaraldehyde treatment, the two nucleotidase enzymes were distinguished from another external surface membrane enzyme, a nonspecific acid phosphatase. Results of the cytochemical assays further demonstrated the biochemical and structural asymmetry of the isolated parasite surface membrane with regard to the localization and distribution of the active sites of these two enzymes.
Mol Biochem Parasitol 1984 Feb
PMID:Surface membrane localization of 3'- and 5'-nucleotidase activities in Leishmania donovani promastigotes. 632 80

Luteal gonadotropin receptors decrease in cows, sheep and rats within 24 h following an injection of a luteolytic dose of prostaglandin (PG) F2 alpha. But it is not known whether this decrease is the specific event, or a reflection of general decline in luteal cell structure, function and metabolism. In order to investigate this possibility, 15 of 21 heifers were given on day 9 of the estrous cycle, a single 500 micrograms injection of Cloprostenol (CO), a synthetic PGF2 alpha analog. These heifers were ovariectomized in groups of 5 at 12, 24 and 36 h after CO. For controls, a group of 6 heifers were ovariectomized just prior to injection of the others. Serum progesterone levels decreased whereas LH levels increased (P less than 0.05) by 12 h with no additional changes observed at 24 or 36 h. The luteal plasma membranes [125I]hCG specific binding, as well as 5'-nucleotidase (5'-NE) activity, decreased by 12 h and continued to decline (P less than 0.05) until 24 h (binding) or 36 h (5'-NE). Scatchard analysis showed that the decrease in [125I]hCG binding was due to a decrease in receptor number rather than a decrease in receptor affinity. The activities of cytochrome c oxidase in mitochondria, NADH cytochrome c reductase in rough endoplasmic reticulum and galactosyl transferase in Golgi decreased while NAD pyrophosphorylase in nuclei virtually disappeared following the injection of CO. The beta-N-acetyl-D-glucosaminidase (a lysosomal hydrolase) activity in the homogenate increased by 12 h and continued to increase up to 36 h.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Cell Endocrinol 1984 Feb
PMID:Decrease of various luteal enzyme activities during prostaglandin F2 alpha-induced luteal regression in bovine. 632 72

During growth and maturation of the tapeworm, Hymenolepis diminuta, significant decreases occur in the brush border membrane-bound alkaline phosphatase, phosphodiesterase, 5'-nucleotidase, adenosine triphosphatase and ribonuclease activities. These decreases are accompanied by qualitative and quantitative changes in the polypeptide profiles of the brush border membrane fraction. Gradients of enzymatic activities and polypeptide profiles are also demonstrable when mature tapeworms are cut into pieces and the brush border membrane of each piece analyzed individually. In fully developed tapeworms the enzymatic activities and polypeptide profiles of membrane preparations reflect mainly the contributions of the more mature proglottids; these proglottids constitute most of the tapeworm biomass. The most anterior sections of these fully developed worms are biochemically similar to young, developing worms.
Mol Biochem Parasitol 1983 Aug
PMID:Alterations in brush border membrane proteins and membrane-bound enzymes of the tapeworm, Hymenolepis diminuta, during development in the definitive host. 663 65

Macrophages have been obtained from the peritoneal cavities of C57BL/6 mice following treatment with C. parvum, MVE-2, mineral oil, or thioglycollate. Cell populations were primarily composed of mononuclear phagocytes as determined by a latex bead uptake assay. Macrophages obtained from C. parvum or MVE-2 were activated as judged by enhanced cytostatic activity against two tumor cell target lines. Thioglycollate-elicited macrophages demonstrated much lower cytostatic ability. Rats were immunized with activated MVE-2 macrophages. Hybridomas were prepared by fusion with a non-secreting myeloma cell line followed by cloning. Cell supernates were selected on the basis of binding to activated but not elicited macrophages. The monoclonal antibody produced has been characterized by flow cytometry. The antibody does not react with syngeneic erythrocytes, thymocytes, or spleen cells. Reaction with thioglycollate macrophages is very low. Alternatively, intense binding is found on activated macrophages. This antigen which accompanies macrophage activation for tumor cell cytostasis is designated as macrophage activation antigen-1 (MAA-1). Several important physiological changes accompany the process of macrophage activation. For example, activated macrophages demonstrate enhanced microbicidal, phagocytic, secretory, and tumoricidal activity (for reviews see refs. 1,2). Concommitant alterations in cell surface properties have been observed. These include: (a) changes in surface morphology and spreading (3-5), (b) altered lipid and protein content (6,7), (c) decreases in 5'-nucleotidase activity and alkaline phosphodiesterase (8), increases in leucine aminopeptidase (8), decreases in mannose receptors (11,12), and antigen F4/80 (11), (d) increases in Ia antigens (11,12), and (e) increased tumor cell binding (13). These structural and functional modifications indicate that activated macrophages represent a unique class of functionally differentiated cells (9). Antigenic modifications accompanying macrophage differentiation are of special interest. Markers for specific macrophage classes might be useful in defining differentiation pathways, dissecting type-specific functional activities such as tumor cytotoxicity, and providing a means to identify macrophage subsets in heterogeneous cell populations. In the present work we have taken the first step in this direction by defining a cell surface macrophage activation antigen.
Mol Immunol 1984 Jul
PMID:Characterization of a monoclonal antibody defining a macrophage activation-specific cell surface antigen. 674 39

Adenosine kinase, adenosine deaminase, hypoxanthine phosphoribosyltransferase, inosine-nucleoside phosphorylase, 5'-AMP deaminase and 5'-IMP nucleotidase were identified in cell-free extracts of duckling erythrocytes; no evidence for 5'-AMP nucleotidase and xanthine oxidase activity was found. The Km values for the duckling red cell enzymes were similar to those reported for human erythrocytes. Plasmodium lophurae extracts demonstrated similar enzyme activities except for 5'-AMP deaminase and 5'-IMP nucleotidase which were absent. It is proposed that during infection erythrocytic AMP is catabolized to IMP, inosine and hypoxanthine; the hypoxanthine is taken up by the plasmodium, utilized to form IMP, and this in turn is converted into adenine and guanine nucleotides.
Mol Biochem Parasitol 1981 Apr
PMID:Purine metabolizing enzymes of Plasmodium lophurae and its host cell, the duckling (Anas domesticus) erythrocyte. 678 22

Adenosine triphosphate metabolism in caudal epididymis bovine spermatozoa was studied. Measurements by HPLC at appropriate time intervals of the spermatozoa content of ATP and its derivatives were carried out under different experimental conditions. In the presence of 2-D-glucose, cellular ATP was transformed almost quantitatively into ADP and AMP at a rate of 2.3 nmol/min per 10(8) cells. At the same time, ADP and AMP accumulated at a rate of 1.52 and 0.58 nmol/min per 10(8) cells, respectively. In the first 4 min, about 50% of total ATP was degraded, the AEC of the cells dropped to non-physiological values while the content of other nucleosides did not vary significantly. Inorganic P(i) content also remained unchanged. Under non-induced conditions up to 240 min, no variations of the adenylic content and of the EC value was observed. Under induced and non-induced conditions, IMP and adenosine were not detected within the spermatozoa. The lack of IMP might be ascribed either to the absence of AMP deaminase, whose activity has never been found in the spermatozoa or to the intracellular environment which down regulates the activity of the enzyme. In order to explain low levels and absence of variations of adenosine, several enzymic investigations were carried out. Adenosine kinase activity was not determined, therefore the transformation of adenosine into AMP had to be excluded. Nevertheless, enzymic activities potentially able to dephosphorylate the formed AMP are present in the spermatozoa. Our findings are indicative of the existence in the spermatozoa of acid and alkaline phosphatase and of 5'-nucleotidase membrane-derived.(ABSTRACT TRUNCATED AT 250 WORDS)
Comp Biochem Physiol B Biochem Mol Biol 1995 Mar
PMID:Adenosine triphosphate catabolism in bovine spermatozoa. 758 34

Hyperthyroidism induces a number of metabolic and physiological changes in the heart including hypertrophy, increase in inotropic status, and alterations of myocardial energy metabolism. The effects of hyperthyroidism on adenosine metabolism which is intimately involved in the control of many aspects of myocardial energetics, have not been clarified. The aim of this study was thus to evaluate the potential role of adenosine in the altered physiology of the hyperthyroid heart. Transport of adenosine was studied in cardiomyocytes isolated from hyperthyroid and euthyroid rats. Activities of different enzymes of purine metabolism were studied in heart homogenates and concentrations of nucleotide and creatine metabolites were determined in hearts freeze-clamped in situ. Both transport of adenosine into cardiomyocytes and the rate of intracellular phosphorylation were higher in the hyperthyroid rat. At 10 microM concentration, adenosine transport rates were 275 and 197 pmol/min/mg protein in hyperthyroid and euthyroid cardiomyocytes respectively whilst rates of adenosine phosphorylation were 250 and 180 pmol/min/mg prot. An even more pronounced difference was observed if values were expressed per number of cells due to cardiomyocyte enlargement. Hyperthyroidism was associated with a 20% increase in adenosine kinase, 30% decrease in membrane 5'-nucleotidase and 15% decrease in adenosine deaminase activities measured in heart homogenates. In addition there was a substantial depletion in the total creatine pool from 63.7 to 41.6 mumol/g dry wt, a small decrease in the adenylate pool (from 27.2 to 24.3 mumol/g dry wt) and an elevation of the guanylate pool (from 1.22 to 1.36). These results show that adenosine transport and phosphorylation capacity is enhanced in hyperthyroidism.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Cell Biochem 1995 Feb 23
PMID:Hyperthyroidism increases adenosine transport and metabolism in the rat heart. 759 49

We have previously demonstrated that exposure of the chick embryo to a 60 Hz, 4 microT split sine wave for the first 72 hours of development causes a significant reduction in the activity of the ectoenzyme 5'-nucleotidase. This reduced activity persisted, throughout the embryonic period, despite further incubation in a field free environment. We also showed that the reduction in 5'NT activity can be localized in the developing brain to the Cerebellum. The present study reveals that superimposition of an electromagnetic noise, of similar amplitude and frequency, can mitigate the effect of the field on 5'NT activity.
Biochem Mol Biol Int 1995 May
PMID:Effectiveness of noise in blocking electromagnetic effects on enzyme activity in the chick embryo. 766 24


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