Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.5.4.4 (adenosine deaminase)
 5,136 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The role of platelets in the maintenance of endothelial barrier is examined in an in vitro model of the microvasculature. Human platelets (6,000/microliters) perfused through a cell column of endothelial-covered microcarriers decrease paracellular permeability of sodium fluorescein (mol wt 342) to 63% of baseline values. This effect is reversible and a second application and removal of platelets produces a similar response. This effect occurs within 5 min and reverses within 10 min after platelet removal. The reduction in permeability is not due to mechanical obstruction of endothelial junctions, since the number of recirculating platelets is not reduced and releasate from unstimulated 2-h platelet incubations also decreases permeability. Releasate from platelets stimulated with 0.1 U/ml of thrombin for 15 min have the same permeability reducing effect. In this system, the platelet factors serotonin (10(-3) M) and ADP (10(-4) M) have no effect on permeability. However, the platelet factors adenosine (10(-4) M), ATP (10(-5) M), and beta-agonists decrease permeability. None of these appear to account for platelet permeability activity, since activity is not blocked by agents directed against these mediators (adenosine deaminase, apyrase, 8-phenyltheophylline, or propranolol). The active factor(s) is stable at -20 degrees C, heat stable, sensitive to trypsin, and has an apparent molecular weight > 100. We conclude that unstimulated platelets release a factor(s) that enhances endothelial barrier in vitro and may be important in maintenance of the normal in vivo barrier.
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PMID:Platelets and a platelet-released factor enhance endothelial barrier. 147 5

Previously, we demonstrated the stimulus-specific ability of platelet lysate or release products to inhibit neutrophil functions in response to f-met-leu-phe (fMLP) or phorbol myristate acetate (PMA). The present study further characterizes these activities and identifies one of the platelet inhibitors of neutrophil superoxide anion (O2-) generation. Sephadex G-200 chromatography revealed two fMLP-specific inhibitory activities in platelet lysate. One component eluted with materials less than 13 kilodaltons (kD) molecular weight, whereas the second fractionated at the void volume (Mr greater than 200 kD). PMA-specific inhibitor(s) cofractionated at the void volume with the lysate's fMLP-inhibitory activity. Release products of activated platelets contained low-molecular-weight (less than 13 kD), fMLP-specific inhibitor activity but failed to demonstrate PMA-specific inhibition of neutrophil O2- generation. Biochemical characterization identified two distinct high-molecular-weight inhibitors in platelet lysate. Pretreatment with adenosine deaminase (ADA) completely abrogated the maximum inhibitory effect (43.8 +/- 7.5%) of the high-molecular-weight, fMLP-specific lysate component but failed to reduce maximum PMA-specific inhibition (93.0 +/- 2.0%) of neutrophil O2- generation. Likewise, while the lysate's fMLP-specific inhibitor was heat stable, heating reduced the PMA-specific inhibition 56.5 +/- 10.4%. Equal sensitivity to ADA, resistance to trypsin, and heat stability were demonstrated by the low-molecular-weight inhibitor(s) in platelet lysate and release products. Neither high- nor low-molecular-weight platelet inhibitors scavenged O2-. High-performance liquid chromatography (HPLC) of the low-molecular-weight inhibitory activity from both platelet lysate and release products revealed physiological levels of adenine nucleotides. Addition of pure adenine nucleotides at physiological levels (1-10 microM) mimicked the effectiveness of the platelet inhibitor. We conclude that stimulus-specific limitation of neutrophil O2- generation by platelet adenine nucleotides may represent a mechanism for reducing inadvertent tissue damage during inflammation.
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PMID:Inhibition of neutrophil superoxide anion generation by platelet products: role of adenine nucleotides. 284 30

A factor (Substance B) has been isolated from brain which reverses the presynaptically-modulated inhibition of evoked ACh release from both guinea-pig myenteric plexus-longitudinal muscle synaptosomes and the intact strip. Inhibitory modulating agents whose activity is reversed by Substance B include oxotremorine, 2-chloroadenosine, clonidine, and morphine. In addition to brain, Substance B is also present in heart and ileum but not in liver or kidney. As determined by Biogel P2 chromatography, this factor appears to have a molecular weight of around 700. It is not destroyed by preincubation with periodate, amylase, adenosine deaminase, pronase, trypsin, phospholipase C or carboxypeptidase Y.
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PMID:Isolation of a factor that reverses presynaptic inhibition of acetylcholine release. 357 23

Incubation of slices of rat cerebral cortical grey matter in Krebs-Ringer bicarbonate-glucose buffer induced a rapid decline in the responsiveness of the adenylate cyclase in subsequently prepared membrane preparations to stimulation by various activators of the enzyme. The loss of responsiveness was time- and temperature-dependent, showed an absolute dependence on extracellular calcium ions, and was mimicked by the presence of serine proteases in the incubation medium. The resultant adenylate cyclase preparation was partially responsive to activation by fluoride and guanylylimidodiphosphate but had become virtually unresponsive to activation by ganglioside, trypsin, or beta-adrenergic agonists. The loss of responsiveness of adenylate cyclase was not altered if slices were incubated with depolarizing agents, putative neurotransmitters, receptor blockers, serine protease inhibitors, or adenosine deaminase. The nature of the calcium-dependent mechanism involved in the loss responsiveness of membranal adenylate cyclase is unknown. A suggested mechanism for the loss of sensitivity is the action of a membrane-bound, calcium-dependent protease.
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PMID:Calcium-dependent desensitization of adenylate cyclase in rat cerebral cortical slices. 625 74

The growth of group A human, bovine, equine and porcine rotaviruses were enhanced by pretreatment of virus with pancreatin, trypsin, protease, alkaline phosphatase or pepsin and incorporation of these enzymes in maintenance medium. In contrast, alpha-amylase or lipase inhibited the growth of equine and porcine rotaviruses. The other enzymes, adenosine deaminase, lactase, lysozyme, ribonuclease or triose-phosphate isomerase gave little or no change in the growth of all four rotaviruses.
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PMID:Effect of enzymes on the growth of human and animal rotaviruses. 754 24

The T-cell activation antigen CD26, is a type II membrane glycoprotein with intrinsic dipeptidyl-peptidase IV (DPP IV) activity, characterized by its capacity to cleave off N-terminal dipeptides containing proline as the penultimate residue. Independent of its catalytic activity, CD26 has also been characterized as adenosine deaminase binding protein. By using CD26 negative human C8166 cells, here we describe the existence of another cell-surface protein which manifests CD26-like DPP IV activity. For convenience, this protein will be referred to as DPP IV-beta. Consistent with the cell-surface expression of DPP IV-beta, intact C8166 cells manifested a high level of DPP IV, whereas, they manifested poor activity against substrates of DPP II known to have an intracellular localization. A partially purified preparation of CD26 from human MOLT4 cells, and the DPP IV-beta expressed on intact cells were found to possess similar catalytic activity and pH optimum. In addition, cell-surface CD26 and DPP IV-beta on intact MOLT4 and C8166 cells, respectively, resisted digestion by proteolytic enzymes such as trypsin and proteinase K. However, adenosine deaminase activity was not detectable on the surface of C8166 cells in contrast to CD26 positive MOLT4 cells. In accord with this, 125I-labeled adenosine deaminase which binds CD26 was found not to bind DPP IV-beta. Gel-filtration experiments using 0.5% Triton X-100 extracts from C8166 and MOLT4 cells, revealed that the apparent molecular mass of DPP IV-beta is 82 kDa, whereas that of CD26 is 110 kDa as expected. Taken together, our results suggest that DPP IV-beta is a CD26-like protein which could be characterized by distinct properties.
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PMID:Dipeptidyl-peptidase IV-beta, a novel form of cell-surface-expressed protein with dipeptidyl-peptidase IV activity. 870 27

The CP-I subunit of calf kidney adenosine deaminase complexing protein (ADCP), isolated by affinity chromatography based on Sepharose-4B immobilized adenosine deaminase, is identical with dipeptidyl peptidase IV. This finding is based on the following results: (a) Its M(r) = 110 kD, as determined by sodium dodecyl sulphate polyacrylamide gel electrophoresis; (b) its catalytic activity toward Gly-Pro-p-nitroanilide; (c) its inhibition by serine protease inhibitor; and (d) by two peptide sequences resulting from its trypsin proteolysis. Accordingly, the CP-I subunit of ADCP isolated from bovine kidney is DPPIV (CD26). Thus, as anticipated, the high affinity between ADA subunits prevails even when they originate in different species.
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PMID:The CP-I subunit of adenosine deaminase complexing protein from calf kidney is identical to human, mouse, and rat dipeptidyl peptidase IV. 962 61

In this study, an attempt was made to elucidate the combined effect of 2'-deoxycoformycin (DCF), an adenosine deaminase inhibitor, with a water extract of Cordyceps sinensis (WECS), on the growth curves of mouse melanoma and lung carcinoma cells. Sub-confluent cells were harvested with an EDTA trypsin solution, and resuspended to appropriate concentrations in DMEM containing 10% fetal bovine serum. Using 1x10(5) cells/2 ml in each well of a 12-well culture plate, cells were incubated for 24, 48 and 72 h in the presence of WECS alone, or WECS plus DCF in a CO2 incubator at 37 degrees C. Duplicate samples of viable cells were enumerated with a Coulter counter. The antitumor effect of WECS on the growth curves of tumor cell lines increased over 3-fold in combination with DCF. These results suggest that DCF has a remarkable reinforcement effect on the antitumor activity of WECS. DCF is a potent adjuvant for WECS.
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PMID:Reinforcement of antitumor effect of Cordyceps sinensis by 2'-deoxycoformycin, an adenosine deaminase inhibitor. 1743 79

Cell culture models are frequently used to study the role of adenosine in several physiological and pathological processes. In the present study, we have shown that adenosine deaminase activity in medium supplemented with calf serum significantly reduces adenosine concentration in culture medium. In the presence of HepG2 cells, the adenosine concentration in culture medium is decreased much faster, because a large amount of exogenous adenosine is metabolized by cellular enzyme. In order to measure intracellular adenosine, inosine, adenine nucleotides, S-adenosylhomocysteine (AdoHcy) and Sadenosylmethionine (AdoMet) contents, two methods for cell harvesting were compared. First, cells were removed with trypsin/EDTA, second, cells were lysed in cell culture dishes immediately after removing culture medium. Our results show that exact determination of adenosine metabolites requires immediate inactivation of metabolism by cell lysis in culture dishes. Application of adenosine (1mM) resulted in a time-dependent increase in intracellular adenosine, inosine, AMP, ATP, AdoHcy and AdoMet concentration. Since AdoHcy levels increased to a larger extent than AdoMet, the methylation potential, expressed as the ratio of AdoMet/AdoHcy, was reduced from 51.8 (control) to 2.9 (adenosine 1 mM, 2 hrs), suggesting that AdoMet-dependent methylation reactions might be impaired. In conclusion our data demonstrate that extracellular adenosine concentration and intracellular metabolite concentration strongly depend on the methods used to culture and harvest the cells.
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PMID:Adenosine metabolism and its effect on methylation potential in cultured cells: methodological considerations. 1754 25