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)

Two forms of adenosine deaminase (adenosine aminohydrolase, EC 3.5.4.4), differing in molecular size, have been purified and obtained in homogeneous form from rabbit intestine. The purification procedures involved extraction with acetate buffer, pH 5.5, precipitation and fractional reextraction with (NH4)2SO4, ion-exchange chromatography on DEAE-cellulose and gel filtration on Sephadex G-75 and Sephadex G-200. Gel filtrations analysis gave molecular weight estimates of 265 000 and 32 000 for the large and small deaminases respectively. The two enzymes forms had similar pH optima and pH stability ranges.
 ...
PMID:Purification of multiple forms of adenosine deaminase from rabbit intestine. 0 39

Adenosine deaminase (adenosine aminohydrolase EC 3.5.4.4) has been purified 468,000-fold from pooled human erythrocytes. The procedure developed was used to isolate the enzyme from up to 23 liters of packed erythrocytes at one time. An easily prepared affinity column bed material employing adenosine as the ligand was used as the final step in the purification. During elution from the affinity column there was approximately a 3:1 partition of adenosine deaminase between gel bed and column buffer. There was no apparent difference in the partitioning of unresolved or partially resolved preparations of the electrophoretically different forms of the enzyme on the affinity column. Gel filtration and electrophoresis on polyacrylamide gels of increasing concentration revealed no differences in the Mr of these electrophoretically different forms. The four bands resolved by electrophoresis of the different forms on polyacrylamide gels under nondenaturing conditions yielded a single band when electrophoresis was carried out in the presence of sodium dodecyl sulfate and 2-mercaptoethanol. Partially resolved preparations of the different electrophoretic forms of adenosine deaminase also gave rise to a single band of the same mobility when electrophoresed on polyacrylamide gels under these conditions. The band had the mobility of a protein of Mr of 36,000. This Mr is approximately the same as estimated for the nondenatured enzyme.
 ...
PMID:Purification of human erythrocyte adenosine deaminase by affinity column chromatography. 93 20

1. The partial purification of adenosine deaminase, types 1, 2 and 2-1, from human erythrocytes is described. 2. The isoenzyme components characteristic of the three forms of the enzyme were partially resolved by chromatography on DEAE-Sephadex. 3. Gel chromatography of the various forms of the enzyme gave estimates of the molecular weights in the range 30000-35000. 4. Electrophoresis in starch gels containing increasing percentages of starch did not reveal any differences in molecular weight between the genetic variants or their isoenzyme components. 5. Analytical isoelectric-focusing experiments in polyacrylamide gels gave the following pI values for the four isoenzyme components present in type 2-1 erythrocytes: 4.70, 4.83, 4.94 and 5.06. 6. All forms of the enzyme gave K(m) values for adenosine of about 30mum and K(i) values of about 8mum for the competitive inhibitor purine riboside. 7. Reaction rates of the type 1 and 2 enzymes were measured at different temperatures. Both enzymes gave values for the energy of activation for hydrolysis of adenosine of about 33.4kJ/mol (8kcal/mol). 8. Heat inactivation of all forms of the enzyme was markedly dependent on ionic strength, the rate of inactivation increasing with increasing ionic strength. The type 1 and type 2 forms of the enzyme differed significantly in their susceptibility to heat inactivation. From the variation of rates of inactivation with temperature, values were obtained for the energies of activation for the heat inactivation of both enzymes as follows: type 1 enzyme 275.5kJ/mol (65.9kcal/mol) and type 2 enzyme 241.6kJ/mol (57.8kcal/mol.).
 ...
PMID:Partial purification and properties of the common inherited forms of adenosine deaminase from human erythrocytes. 472 18

Binding of adenosine to S-adenosyl-L-homocysteine (AdoHcy) hydrolase (EC 3.3.1.1.) and partial conversion of bound adenosine to a substance liberating adenine has been demonstrated under conditions of enzymatic synthesis and hydrolysis of ADoHcy (Ueland, P. M., and Helland, S. (1980) J. Biol. Chem. 255, 7722-7727). Gel filtration of cytosol from isolated rat hepatocytes treated with [14C]adenosine on a high performance liquid chromatography protein column showed that labeled adenine/adenosine eluted as a peak which co-chromatographed exactly with AdoHcy hydrolase. Formation of this peak was inhibited by exposure of the cells to compounds (ara-A, 3-deazaadenosine, and homocysteine) interacting with the catalytic site of the enzyme. Furthermore, the adenine/adenosine-protein complex and AdoHcy hydrolase focused at exactly the same pH (pI = 5.76) in a granulated bed. On this basis it was concluded that labeled adenosine formed a stable complex with AdoHcy hydrolase. A substantial portion (about 50%) of endogenous adenosine in rat hepatocytes seemed to be associated with AdoHcy hydrolase, and this portion equaled the amount of cellular adenosine which was not readily mobilized by high level of extracellular adenosine deaminase. Exposure of the hepatocytes to compounds which block the formation of the adenosine-AdoHcy hydrolase complex (ara-A, 3-deazaadenosine, and homocysteine) for 1 to 2.5 h only slightly reduced the amount of adenosine associated with the enzyme, indicating a slow turnover of the complex under the conditions of the experiment. It was concluded that adenosine is sequestered in rat hepatocytes through the interaction with AdoHcy hydrolase. The physiological implication of this process may be related to the metabolism and biological effects of adenosine as well as the regulation of AdoHcy hydrolase activity.
 ...
PMID:Binding of adenosine to intracellular S-adenosylhomocysteine hydrolase in isolated rat hepatocytes. 682 9

Gel filtration of human thyroid extract with Sephadex G-200 revealed two molecular forms of adenosine deaminase differing in their molecular sizes. The smaller form of adenosine deaminase was purified over 120-fold by precipitation of the protein impurities at pH5.6 and chromatography on DEAE-Sephadex A-50, Sephadex G-100 and adenosine-Sepharose. The purified enzyme was specific towards adenosine. The Michaelis constant was 5.2 X 10(-5) M. The optimum pH was about 7.0 and molecular weight 42000.
 ...
PMID:Adenosine deaminase from human thyroid purification and some properties. 748 36

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.
 ...
PMID:Dipeptidyl-peptidase IV-beta, a novel form of cell-surface-expressed protein with dipeptidyl-peptidase IV activity. 870 27

By using a CD26 negative human lymphoblastoid cell line (C8166), here we describe the characterization of a cell-surface protein which manifests CD26-like dipeptidyl peptidase IV (DPP IV) activity. This protein, referred to as DPP IV-beta, shows a higher KM value for Gly-Pro-pNA than CD26 (0.31 mM compared to 0.11 mM, respectively). In addition, DPP IV-beta was found not to bind 125I-labeled adenosine deaminase (a property of human CD26). Gel filtration experiments using extracts from C8166 and MOLT4 (a CD26 positive human T cell line) cells, revealed that the apparent molecular mass of DPP IV-beta is 82 kDa, whereas that of CD26 is 110 kDa. In order to conveniently differentiate both activities, a new family of inhibitors, that selectively blocks peptidase activity associated to CD26, has been developed.
 ...
PMID:Further characterization of DPP IV-beta, a novel cell surface expressed protein with dipeptidyl peptidase activity. 933 Jun 97

RNA editing by members of the ADAR (adenosine deaminase that acts on RNA) enzyme family involves hydrolytic deamination of adenosine to inosine within the context of a double-stranded pre-mRNA substrate. Editing of the human GluR-B transcript is catalyzed by the enzyme ADAR2 at the Q/R and R/G sites. We have established a minimal RNA substrate for editing based on the R/G site and have characterized the interaction of ADAR2 with this RNA by gel shift, kinetic, and cross-linking analyses. Gel shift analysis revealed that two complexes are formed on the RNA as protein concentration is increased; the ADAR monomers can be cross-linked to one another in an RNA-dependent fashion. We performed a detailed kinetic study of the editing reaction; the data from this study are consistent with a reaction scheme in which formation of an ADAR2.RNA ternary complex is required for efficient RNA editing and in which formation of this complex is rate determining. These observations suggest that RNA adenosine deaminases function as homodimers on their RNA substrates and may partially explain regulation of RNA editing in these systems.
 ...
PMID:Adenosine to inosine editing by ADAR2 requires formation of a ternary complex on the GluR-B R/G site. 1216 87