Muscle AMP aminohydrolase. II. Distribution of AMP aminohydrolase, myokinase and creatine kinase activities in skeletal muscle.
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Adenine Nucleotides↗
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[Functional importance of catecholamine metabolism in the regulation of AMP-aminohydrolase activity in mitochondria of the heart and other organs].
The paper deals with main pathways for conversion of catecholamines and their effect on the activity of AMP-aminohydrolase in mitochondria of the heart, liver, brain, kidneys and blood serum. Dopamine-beta hydroxylase is stated to participate in manifestation of dopamine effect on the heart AMP-aminohydrolase, the same may be said with respect to monoaminooxidase in realization of the norepinephrine action on the brain AMP-aminohydrolase. Adrenoxyl (stabilized adrenochrome) duplicates the catecholamine effect with respect to AMP-aminohydrolase in certain organs. A three-hour electric stimulation of the aorta arc is accompanied by activation of AMP-aminohydrolase in the heart and blood serum, which is, probably, associated with changes in the balance and metabolism of tissue catecholamines. Data of the AMP-aminohydrolase activity determination may be applied for testing the myocardium damage. AMP-aminohydrolase is discussed for its role in realization of the adrenochrome effect on the myocardium adenylate cyclase.
AMP Deaminase↗
Interaction of AMP-aminohydrolase with myosin and its subfragments.
We have shown that purified rabbit skeletal muscle AMP-aminohydrolase binds to rabbit muscle myosin, heavy meromyosin, and Subfragment 2 but does not bind to light meromyosin nor to Subfragment 1. The dissociation constant for binding to myosin was determined to be 0.14 muM. A new sedimentation boundary, presumably reflecting formation of a complex between AMP-aminohydrolase and heavy meromyosin or Subfragment 2, can be observed using the analytical ultracentrifuge. Binding of AMP-aminohydrolase to myosin, heavy meromyosin, or Subfragment 2 is abolished by phosphate (less than 10 mM), an inhibitor of AMP-aminohydrolase. No other rabbit muscle enzyme tested showed any interaction with myosin under the same conditions and there was no indication of complex formation between AMP-aminohydrolase and phosphofructokinase or phosphocreatine kinase in the analytical ultracentrifuge.
AMP Deaminase↗
Characteristics of an aminohydrolase distinct from adenosine deaminase in cultured human lymphoblasts.
An inherited deficiency of adenosine deaminase (adenosine aminohydrolase, EC 3.5.4.4) is associated with an autosomal recessive form of severe combined immunodeficiency disease. Affected patients exhibit markedly reduced or absent adenosine deaminating activity in various tissues. In this study we have demonstrated the presence of a low level aminohydrolase activity in 11 different normal and adenosine deaminase-deficient lymphoblast cell lines which is apparently distinct from normal adenosine deaminase. Based on enzymatic, physical and immunoreactive properties, this lymphoblast aminohydrolase does not appear to be related to adenosine deaminase and is most likely coded for by a different gene locus. In future investigations designed to characterize mutant forms of adenosine deaminase, it will be important to distinguish this lymphoblast aminohydrolase activity from putative products of the adenosine deaminase gene locus.
Adenine↗
Adenosine-aminohydrolase activity in the erythrocytes, lymphocytes, and plasma of healthy subjects and kidney transplant recipients.
Adenosine-aminohydrolase activity in the red blood cells and lymphocytes of transplant patients were assayed by continuous flow analysis. This enzyme, which has been implicated in the ability of lymphocytes to mount an immune response, was evaluated in renal allografted patients immunosuppressed by azothiprine and methylprednisone. Red cell adenosine-aminohydrolase activity was depressed in all patients when compared to nontreated health controls. Adenosine aminohydrolase activity was raised in the lymphocytes of the renal allografted patients. Renal transplant patients' in vitro lymphocyte reactivity to antigens, mitogens, or skin testing to specific antigens, confirmed the depressive effects of immunosuppression observed in vivo. We conclude from these studies that red cell adenosine-aminohydrolase activity may be a more sensitive index of the state of immunoresponsiveness than the corresponding enzyme activity in the lymphocyte.
Adenosine Deaminase↗
[AMP-aminohydrolase of the brain and other organs and the regulation of its activity].
Present concepts of the hydrolytic deamination of adenylic acid through AMP-aminohydrolase of brain and other tissues are discussed. The content of AMP-aminohydrolase of tissues, its intracellular disposition, physico-chemical properties, physiological role and the regulation of its activity are considered. AMP-aminohydrolase of brain is compared with that of other tissues (muscle, liver, kidney, erythrocytes, etc.), and characteristic features of the regulation of its activity in brain tissue is included. The participation of nucleotides, phosphoorganic compounds, hexokinase and some cations in the regulation of AMP-aminohydrolase activity of brain and other tissues are discussed on the basis of the experiments carried out and the data available.
AMP Deaminase↗
Circulatory clearance, internalization, and degradation of muscle AMP aminohydrolase.
Chicken muscle AMP aminohydrolase is cleared rapidly from the circulation of chickens after intravenous injection of the purified enzyme (Husic, H. D., and Suelter, C. H. (1980) Biochem. Biophys. Res. Commun. 95, 228-235). After the intravenous injection of unlabeled, 125I-labeled, or [14C]sucrose-labeled AMP aminohydrolase, enzyme activity and radioactivity are cleared at the same rates and concentrate in the liver and spleen. After injection of the [14C]sucrose-labeled enzyme, 14C is retained in the liver and spleen and low molecular weight 14C is recovered primarily in a fraction which cosediments with lysosomes when tissue homogenates are sedimented on sucrose density gradients. When liver cells are fractionated after clearance of [14C]sucrose-labeled enzyme, 14C is recovered primarily in the parenchymal cells. The circulatory clearance of AMP aminohydrolase is inhibited by heparin and other sulfated polysaccharides, but not by compounds which inhibit previously described carbohydrate-mediated systems for the uptake of circulatory glycoproteins. Heparin injection after the clearance of AMP aminohydrolase causes the release of the enzyme from the liver and spleen into the circulation. When heparin is injected at various times after clearance, decreasing amounts of enzyme are released with time; these results show that the enzyme is internalized with a half-life of 0.98 h.
AMP Deaminase↗
Binding, internalization, and degradation of AMP aminohydrolase by avian hepatocyte monolayers.
Chicken muscle AMP aminohydrolase is cleared from the circulation of chickens after intravenous injection of the purified enzyme with a half-life of 3-5 min (Husic, H.D., and Suelter, C.H. (1980) Biochem. Biophys. Res. Commun. 95, 228-235). The enzyme is not inactivated before clearance, the clearance is inhibited by sulfated polysaccharides, and the enzyme is cleared primarily by the spleen and the parenchymal cells of the liver where it is internalized and degraded in lysosomes (Husic, H.D., and Suelter, C.H. (1984) J. Biol. Chem. 259, 4359-4364). The binding of AMP aminohydrolase to hepatocyte monolayers in vitro at 4 degrees C is saturable with a dissociation constant of 11.3 X 10(-8) M; there are 2.6 X 10(6) AMP aminohydrolase binding sites/hepatocyte. The interaction of the enzyme with hepatocyte monolayers is inhibited by sulfated polysaccharides, effectors of its enzymatic activity and high salt concentrations; various monosaccharides had little effect on the binding of the enzyme to hepatocyte monolayers. Heparitinase treatment of hepatocyte monolayers abolished 77% of the binding of the enzyme. Heparin promotes the dissociation of 125I-labeled or [14C]sucrose-labeled enzyme bound to the cell surface; radioactivity which is not dissociated by heparin is assumed to be internalized at 37 degrees C. Low molecular weight 125I-labeled degradation products are released into the media with time when the 125I-labeled enzyme, bound to hepatocytes at 4 degrees C, is incubated at 37 degrees C; when [14C]sucrose-labeled enzyme is incubated with hepatocytes at 37 degrees C, low molecular weight 14C-labeled degradation products are not released into the media but instead accumulate in the cells. The half-life for internalization of the bound enzyme based on this rate of accumulation is 0.77 h. These results suggest that glycosaminoglycans are involved in the binding of AMP aminohydrolase to the hepatocyte cell surface and that the bound enzyme is internalized and degraded.
AMP Deaminase↗
Cloning and comparison of the DNA encoding ammelide aminohydrolase and cyanuric acid amidohydrolase from three s-triazine-degrading bacterial strains.
DNA encoding the catabolism of the s-triazines ammelide and cyanuric acid was cloned from Pseudomonas sp. strain NRRLB-12228 and Klebsiella pneumoniae 99 with, as a probe, a 4.6-kb PstI fragment from a third strain, Pseudomonas sp. strain NRRLB-12227, which also encodes these activities. In strains NRRLB-12228 and 99 the ammelide aminohydrolase (trzC) and cyanuric acid amidohydrolase (trzD) genes are located on identical 4.6-kb PstI fragments which are part of a 12.4-kb DNA segment present in both strains. Strain NRRLB-12227 also carries this 12.4-kb DNA segment, except that a DNA segment of 0.8 to 1.85 kb encoding a third enzyme, ammeline aminohydrolase (trzB), has been inserted next to the ammelide aminohydrolase gene with the accompanying deletion of 1.1 to 2.15 kb of DNA. In addition, the s-triazine catabolic genes are flanked in strain NRRLB-12227 by apparently identical 2.2-kb segments that are not present in the other two strains and that seem to cause rearrangements in adjacent DNA.
Amidohydrolases↗
[Molecular forms of guanine aminohydrolase (author's transl)].
Guanine aminohydrolase (E.C. 3.5.4.3) has been purified 11-fold from the supernatant fraction of guinea-pig liver homogenates in 0.25 M sucrose (centrifuged at 50,000 X g) through thermic denaturation at 60 degrees C and ammonium sulphate fractionation (30--60% saturation). The enzyme in the homogenates and purified preparations exhibited two Km values. In both preparations four enzymatic electrophoretic bands have been detected. Purified guanine aminohydrolase is chromatographically resolved on DEAE-sephadex in three components whose active forms appeared separately on their pherograms. The enzymatic form eluted at lower ionic strength has the least anodic mobility, is inhibited by guanine (4 X 10(-5) M) and presents only one Km value (1.5 X 10(-5) M). The enzymatic form eluted at greater ionic strength exhibits the highest anodic mobility, is also inhibited by guanine (7 X 10(-5) M) and its Km value seems to be 6.3 X 10(-6) M. Molecular weight of enzymatics forms determined by Sephadex G-200 chromatography, is 120,000 +/- 5,000. The preceding results, correlated with the chromatographic homogeneity of guanine aminohydrolase, purified in Sephadex G-100, suggests that the four molecular forms of the native enzyme may be considered as isozymes.
Aminohydrolases↗
[AMP-aminohydrolase activity of the nuclear fraction of rat brain].
AMP-aminohydrolase activity has been found not only in mitochondrial and soluble fractions but also in nuclear fraction of rat brain. The regulation of nuclear AMP-aminohydrolase activity differs from that of mitochondrial and soluble fractions. 1. Hexokinase does not enhance deamination of AMP in intact nuclei while it activates the enzyme in extracts of acetone powder of nuclear fractions. 2. The AMP-aminohydrolase activity of rat brain nuclear fraction is considerably inhibited by GTP and phosphate but in contrast to other fractions the stimulatory effect of ATP on enzyme activity is preserved.
AMP Deaminase↗
Guanine aminohydrolase in rat and mouse red cells: a potent inhibitor of guanylation of tRNA.
1. The red blood cells of mice and rats contained guanine aminohydrolase (EC 3.5.4.3). This enzyme was not present in rabbit, sheep or human red blood cells. 2. The enzyme from rat blood cells was separated into two activities by column chromatography on DEAE-cellulose. Both isozymes were labile but it was possible to show that the more abundant enzyme followed Michaelis-Menten kinetics, had an apparent Km of 4.0-10-6 M and was not activated by GTP nor inhibited by allantoin. 3. We believe, therefore, that guanine aminohydrolase was the protein in rat and mouse red blood cells that inhibited the enzyme (in rabbit reticulocytes) responsible for guanylation of tRNA.
Aminohydrolases↗
Study of adenine aminohydrolase in the yeast, Schizosaccharomyces pombe.
Observation of the growth of some adenineless mutants of Schizosaccharomyces pombe on six substituted purine analogs leads to the hypothesis that an enzyme is present which catalyzes the conversion of these analogs into hypoxanthine. The enzyme adenase (adenine aminohydrolase, EC 3.5.4.2) has been found to be active in cell-free extracts of S. pombe. Results are reported which are in agreement with the hypothesis that this enzyme is responsible for the in vivo utilization of 6-chloropurine. This evidence comes mainly from a study of adenine aminohydrolase in two mutants selected for partial inability to grow on 6-chloropurine.
Adenine↗
[Liver and brain guinea-pig guanine aminohydrolase (author's transl)].
Guinea-pig brain guanine aminohydrolase (E.C. 3.5.4.3) (M = 120,000 +/- 5,000 daltons) only exhibited one active electrophoretic band; its mobility is similar with that observed for the guinea-pig liver molecular form III. Both forms appear to have coincident activity with pH, as well as an analogous thermal stability and Km values with different substrates showing a different behaviour with the molecular form I of guinea-pig liver enzyme. Brain guanine aminohydrolase and liver molecular form III have similar pK'a values suggesting the participation of histidine and cysteine (-SH) in the enzymatic catalysis. The competitive inhibition by p-chloromercuribenzoate may corroborate the intervention of the last-one.
Aminohydrolases↗
[Structural requirements of guanine aminohydrolase (author's transl)].
Structural requirements of substrates and inhibitors of guinea-pig brain guanine aminohydrolase (GAH; E.C. 3.5.4.3), have been established by working with guanine analogs (8-azaguanine, 1-methylguanine, thioguanine and guanosine), purine precursors (5-aminoimidazole-4-carboxamide), purinic bases (xanthine, hypoxanthine, adenine and uric acid) and pyrimidinic bases (citosine, thymine and uracil). The need of the purine ring for the compounds to behave as substrate has been shown. The carbonyl group placed in position 6, plays an essential role in purine and pyrimidine binding to the enzymatic molecule. 5-aminoimidazole-4-carboxamide and allopurinol are enzyme inhibitors, while guanosine, thioguanine and 2,6-diaminopurine are not. Groups in positions 2, 6, 7 and 9 play a significant role in the union of the guanine molecule with guanine aminohydrolase.
Aminohydrolases↗
Cosolvent-buffer mixtures as models for the cytoplasmic mileu: the enzymology of adenosine aminohydrolase.
Adenosine aminohydrolase from calf intestinal mucosa is sensitive to changes in its environment produced by small mole fractions of dimethylsulfoxide (DMSO). At a mole fraction of 0.1 where the dielectric constant is lowered from that of 78 of neat water to about 76.5, Vmax was reduced by 65% and affinity for substrate (adenosine) and the two competitive inhibitors, insine and N6-benzyladenosine, was decreased markedly. However, this decreased affinity was such that Ki/Km remained virtually constant for both inhibitors. DMSO itself showed the kinetics of a mixed inhibitor with Ki decreasing with increasing mole fraction. This cosolvent also decreased the heat stability of the enzyme which suggests that enzyme conformation is altered by DMSO. Comparison of data in the presence of DMSO with previously obtained data with dioxane shows that heat stability as well as Vmax, at a given value of dielectric constant, is independent of the amount or nature of cosolvent used to achieve that dielectric constant. However, cosolvent induced changes in Ki indicate that colligative as well as dielectric constant effects contribute to the observed changes in kinetic behavior. These experiments may be considered as models for the behavior of enzymes in the medium of lowered dielectric constant expected in the vicinity of cytoplasmic membranes. The results indicate that in such an environment, adenosine aminohydrolase would be expected to be less efficient a catalyst, but equally susceptible to product inhibition, as compared to media of dielectric constant approaching that of water.
Adenosine Deaminase↗
Adenosine aminohydrolase activity in the regenerating rat liver.
The specific activity of adenosine aminohydrolase in the regenerating rat liver is significantly increased 12 h after partial hepatectomy. There is a twofold increase in enzyme activity at 48 h, after which the activity begins to decline. However, increased values still persist 7 days postsurgery. The enzyme is located mainly in the soluble supernatant (90-95%) of the cell. The purified enzyme from 48-h regenerating liver and control liver has similar kinetic properties (Km 54-58 microM for adenosine), similar molecular weights (30,000-35,000), and are equally inhibited by an irreversible transition-state analog and a reversible competitive inhibitor. It is concluded that adenosine aminohydrolase in regenerating liver is an integral component of a salvage pathway designed for the reutilization of nucleotides, and thus helps maintain a "growth state" for the regenerating liver.
Adenosine Deaminase↗
Allosteric modifier and substrate binding of donkey deoxycytidylate aminohydrolase (EC 3.5.4.12)
The hexameric allosteric enzyme deoxycytidylate aminohydrolase from donkey spleen is shown by equilibrium dialysis to bind specifically the allosteric inhibitor, dTTP, the activator dCTP, and the substrate analog dAMP each at six sites (the dTTP and dCTP sites may or may not be identical). These conclusions contrast with earlier ones that there were four sites for each effector; reasons for the discrepancy are discussed. With the knowledge of site numbers and the kinetic information from the accompanying paper it is concluded that the kinetic cooperativity of the enzyme excludes a concerted conformational transition mechanism. Amino acid analysis gives a molecular weight of 18,842 Da per subunit, i.e., 113,052 for the hexamer. A new simplified purification of homogeneous enzyme from donkey spleen probably useful for dCMP aminohydrolase from other sources is described.
Adamantane↗