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PubMed1977

5'-AMP aminohydrolase activity in erythrocytes from normal and dystrophic individuals.

5'-AMP aminohydrolase activities in red blood cells from normal human adults and from patients with pseudohypertrophic dystrophy, myotonic dystrophy, limb girdle dystrophy, neuromuscular atrophy, Charcot-Marie Tooth Disease, and spinal muscular atrophy were examined. In contrast to the greatly decreased skeletal muscular levels of 5'-AMP aminohydrolase observed in Pseudohypertrophic muscular dystrophy, levels in red blood cells of all patients were not significantly different from normals. Pyruvate kinase and creatine kinase activities were determined for comparative purposes. The density distribution of normal and dystrophic erythrocytes were essentially identical.

AMP Deaminase↗
PubMed1984

dCMP-aminohydrolase activity during early sea urchin development. An example of negative enzyme control during embryogenesis.

In sea urchin, unfertilized eggs have a very high level of dCMP-aminohydrolase (dCMPase) activity, which decreases gradually and at the pluteus stage it is only about a quarter of that found in the unfertilized egg. But in abnormal embryos and in disaggregated cells from embryos, no decrease in the dCMPase activity takes place. To understand the control mechanism involved in this enzyme activity during development, we have analyzed the effect of various drugs which interfere with information transfer, such as actinomycin C, puromycin, 5-azacytidine, 2-thio-uracil and p-fluoro-DL-phenylalanine on dCMPase activity in embryos of Paracentrotus lividus and Sphaerechinus granularis. Among these drugs only actinomycin induces a remarkable increase of the dCMPase activity in embryos with respect to unfertilized eggs. Puromycin has a differential and dose-dependent effect. Other drugs, although they affect normal development and macromolecular synthesis, do not significantly alter the dCMPase activity. On the basis of these results we suggest the presence of a repressor mechanism in the control of dCMP-aminohydrolase level during early embryogenesis of sea urchin.

Animals↗
PubMed1979

Adenine aminohydrolase: occurrence and possible significance in trypanosomid flagellates.

Adenine aminohydrolase (EC 3.5.4.2) from four species of Leishmania and from Crithidia fasciculata was examined for specific activities, affinity for substrate (adenine), and stability to heat. All were found to be strongly and non-competitively inhibited by both coformycin and deoxycoformycin, two tight-binding inhibitors of adenosine deaminase (adenosine aminohydrolase, EC 3.5.4.4). Deoxycoformycin is the more potent inhibitor of the two. Neither inhibitor was active against the purine phosphoribosyltransferases. When deoxycoformycin was added to the defined growth medium containing hypoxanthine as the purine source, the growth of C. fasciculata was unaffected, but when adenine was the purine source for the organism, severe inhibition resulted. This implies that hypoxanthine is the obligatory base for nucleotide synthesis and that the adenine phosphoribosyltransferase (AMP:pyrophosphate phosphoribosyltransferase, EC 2.4.2.7) is, in some manner,idenied access to exogenous substrate.

Adenosine Deaminase↗
PubMed1990

Deoxycytidylate aminohydrolase activity in the Novikoff hepatoma is dependent on the localization of the tumor.

The activity of deoxycytidylate aminohydrolase, a pivotal enzyme for pyrimidine biosynthesis in mammalian tissue, is 100x greater in the Novikoff hepatoma harvested from the intraperitoneal cavity than in the same tumor excised from either subcutaneous or intramuscular sites. The increased enzyme activity in the intraperitoneal tumor is not due to an increase in protein synthesis, since there are no significant differences in enzyme activity between normal liver, and either the subcutaneous or intramuscular hepatomas. Evidence is presented which indicates that deoxycytidylate aminohydrolase activity, and the expression of alternate pathways of pyrimidine biosynthesis in the Novikoff hepatoma, is dependent on the localization of the tumor within the host.

Animals↗
PubMed1976

Adenosine aminohydrolase from human spleen: partial purification and some kinetic properties.

Adenosine aminohydrolase from human spleen was purified 120 fold. In pH 7.3 phosphate buffer at 37 degrees, this enzyme preparation deaminated adenosine and arabinosyladenine (ara-A) with apparent values for the Michaelis constant of 40 muM and 90 muM respectively. The products of both deamination reactions, i.e., inosine and arabinosylhypoxanthine, were competitive inhibitors with Ki equal to 710 muM and 60 muM, respectively. N6-benzyladenosine and 2'-deoxy-N6-benzyladenosine were competitive inhibitors. The former was better able to inhibit ara-A than adenosine deamination, while the latter was equivalent in inhibiting deamination of these two substrates. Evidence for a naturally occurring adenosine aminohydrolase inhibitor in spleen was presented. It is suggested that benzyladenosine and deoxybenzyladenosine might potentiate ara-A chemotherapy of neoplasms and metastates in the spleen and other hemic cells.

Adenosine↗
PubMedDate not supplied

[Various properties of immobilized AMP-aminohydrolase].

Properties of immobilized AMP-aminohydrolase from rabbit muscles are studied. The enzyme retains its activity for a year, is stable under manifold treatment with the substrate or under single treatment with 1 M NaCl which contains 50% ethylene glycol or 10% isopropanol and under treatment with 5 M K2 HPO4 (pH 8.5). The established pH-optimum (6.5-7.0) and the temperature optimum (30-40 degrees C) for immobilized AMP-aminohydrolase as well as inhibition of its activity by Co2+, Cd2+, Zn2+ and n-chloromercury benzoate indicate similarity of its properties with those of the purified enzyme.

AMP Deaminase↗
PubMedDate not supplied

[Kinetic characteristics and effect of sodium fluoride on AMP-aminohydrolase from rat liver hyaloplasm].

NaF in various concentrations is shown to have different effects on the rat liver AMP-aminohydrolase. At constant initial level of AMP in samples the NaF 5-25 mM concentrations favour the enzyme activation and the NaF 5-150 mM concentrations inhibit the AMP deamination. The character of sodium fluoride effect is also determined by the substrate concentration in samples. With the presence of 2-10 mM of AMP and 15 mM sodium fluoride in the reaction mixture the AMP-aminohydrolase activity rises. With the rise of the substrate concentration in the sample the positive kinetic cooperation is replaced by the negative one. The maximal reaction rate is reduced. The Hill coefficient in the control and in the sample with 15 mM of NaF is identical and equals 2.5.

AMP Deaminase↗
PubMedDate not supplied

[Determination of AMP-aminohydrolase activity by a chromatographic method].

A method is developed for determining the AMP-aminohydrolase activity by means of chromatography on the home KY-2 ion-exchange resin. It differs from the method of differential spectrophotometry by the fact that its application enables the content of IMP formed due to the enzymic reaction to be determined by its absolute quantity. This method yields satisfactory results independently of the substrate concentration. However, it cannot be applied for determination of the AMP-aminohydrolase activity in the presence of ATP.

AMP Deaminase↗
PubMed1984

Studies of rabbit brain, intestine and liver guanine aminohydrolase.

Guanine aminohydrolase (EC 3.5.4.3) from rabbit brain, intestine, and liver has been purified to homogeneity by affinity chromatography at room temperature and 0-4 degrees C. In all cases the recovery and fold purification was greatest for purification at room temperature. Each enzyme has a subunit mol. wt of 49,500 and crosslinking studies revealed the native form to be a dimer. The amino acid analysis showed a high content of asx, glx, ser, gly and leu; the pI was 5.0 for each prep. The Michaelis constants at pH 8.0 were 6.1, 6.1 and 5.8 X 10(-6) M for brain, intestine and liver GAH respectively. The enzymes had a broad pH activity profile with an optimum of pH 8.0-8.5.

Amino Acids↗
PubMed2006

N6-methyl-AMP aminohydrolase activates N6-substituted purine acyclic nucleoside phosphonates.

In this study we present the identification and characterization of the enzyme involved in the N6-cyclopropyl-2,6-diamino-9-[2-(phosphonomethoxy)ethyl]purine (N6-cyclopropyl-PMEDAP) conversion to biologically active 9-[2-(phosphonomethoxy)ethyl]guanine (PMEG) as well as abacavir 5'-phosphate to carbovir 5'-phosphate. This enzyme was purified from rat liver to homogeneity; it appears to be composed from six 42 kDa subunits and its native form has the molecular weight 260 kDa. This so far unknown enzyme catalyzes conversion of both N6-methyl-AMP and N6-methyl-dAMP to IMP and/or dIMP, respectively. The enzyme acts as 6-(N-substituted amino)purine 5'-nucleotide aminohydrolase with the reaction mechanism very similar to AMP deaminase. The enzyme does not deaminate AMP and dAMP, or the corresponding nucleosides. It is inhibited by deoxycoformycin 5'-phosphate but not by deoxycoformycin or erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA).

Adenine↗
PubMed1981

Agarose-linked xanthosine: a biospecific resin for guanine aminohydrolase.

Polymer-bound xanthosine (4) has been prepared. Condensation of xanthosine with ethyl 4-oxovalerate and saponification of the product gave 2',3'-O-[1-(2-carboxyethyl)ethylidene] xanthosine. The latter was coupled to 6-aminohexylagarose through its carboxylic group, to yield the polymer 4. The content of bound ligand was 8 mumol/g of moist gel, a value that agrees with the number of free amino groups determined by the trinitrobenzenesulfonic acid assay before coupling. Immobilised xanthosine was used as a biospecific resin (inhibitor resin) for guanine aminohydrolase (EC 3.5.4.3), to separate the enzyme from a mixture containing adenosine deaminase (EC 3.5.4.4).

Adenosine Deaminase↗
PubMed1975

Purification of rabbit liver guanine aminohydrolase.

Rabbit liver guanine aminohydrolase has been purified 1250-fold by utilization of an affinity chromatographic separation on 9-(p-aminoethoxyphenyl) guanine-Sepharose with 50% recovery of activity. Polyacrylamide gel electrophoresis of the purified preparations revealed several protein bans which corresponded to regions of enzyme activity measured on gels which had been run under the same conditons. Gel concentration studies of the protein migration rate showed that the protein bans differed in molecular size. The minimum molecular weight was 100,000 from gel permeation chromatography studies. The pH optimum was near pH 8 and the Km, with guanine as substrate was 5.6 x 10-6 M. The latter values are in close agreement with partially purified preparations described in the literature.

Aminohydrolases↗
PubMed1969

Deoxycytidine and radiation response: exceedingly high deoxycytidine aminohydrolase activity in human liver.

The activity of deoxycytidine aminohydrolase in the liver of various species including man was investigated. An enormously high activity was found in human liver. This fact explains the extraordinarily low level of deoxycytidine in human urine in comparison with that of other tested species. The suitability of deoxycitidinuria as a biochemical indicator of postirradiation damage in man remains, therefore, an open question.

Adult↗
PubMed1994

Interaction of the high-affinity inhibitor tetrahydro-dUMP with the allosteric enzyme deoxycytidylate aminohydrolase.

Tetrahydro-dUMP, an analog of the putative transition state in aminohydrolysis of deoxycytidine monophosphate (dCMP) inhibits the allosteric enzyme deoxycytidylate aminohydrolase with high affinity. The inhibition is reversible, and its kinetics is consistent with the analog binding at the substrate site only to one and the same conformation that binds the substrate dCMP. Such kinetics is what would be expected for a transition state analog interacting in an allosteric "K system."

Allosteric Regulation↗
PubMed1991

Hill coefficient ratios give binding ratios of allosteric enzyme effectors; inhibition, activation, and squatting in deoxycytidylate aminohydrolase (EC 3.5.4.12)

The ratio of the steady-state kinetic Hill coefficients of two different effectors equals (under some rather weak general assumptions) the ratio in which the effectors displace each other from an enzyme. This principle can make implications of experimental allosteric enzyme kinetic data immediately apparent. We can use it to find that one molecule of the allosteric inhibitor of dCMP aminohydrolase, at moderately high effector concentrations, displaces one molecule of substrate, or one molecule of activator, whereas at very high concentrations, one molecule of inhibitor displaces two of substrate. Further use of the principle suggests that substrate, at high concentrations, binds binds to activator sites. However, ratios of substrate, activator, and inhibitor Hill coefficients are incompatible with a simple model of activation in which substrate and activator are bound to the same conformation.

Allosteric Regulation↗
PubMed1976

Specific modification of the GTP binding sites of rat 5'-adenylic acid aminohydrolase by periodate-oxidized GTP.

1. Rat skeletal muscle AMP deaminase (AMP aminohydrolase, EC3.5.4.6) can be inactivated by incubation with the periodate-oxidized analogue of the enzyme inhibitor GTP. 2. Nucleoside triphosphates and KCl at high concentrations protect against inactivation, while ADP has no effect. 3. The inactivation can be reversed by the addition of GTP and amino acids and made irreversible by reduction with NaBH4. This indicates that, in the binding of the oxidized GTP to the enzyme, a Schiff base is formed between the aldehyde groups of the inhibitor and amino groups of the enzyme. 4. The kinetic properties of the reduced (oxidized GTP)-AMP deaminase derivative indicate that the loss of activity results from an increase in Km while no appreciable change in V is observed; consequently, the enzyme shows positive homotropic cooperativity even in the presence of optimal KCl concentration. 5. Since the treated enzyme shows kinetic properties similar to those of the native enzyme in the presence of GTP, and since the loss of sensitivity to GTP is directly proportional to the degree of inactivation, it is concluded that the oxidized GTP specifically modifies the binding sites for GTP. 6. Binding of the radioactive oxidized GTP shows that two binding sites for this reagent exist in the AMP deaminase molecule.

AMP Deaminase↗
PubMed1994

(R)-5-fluoro-5,6-dihydrouracil: kinetics of oxidation by dihydropyrimidine dehydrogenase and hydrolysis by dihydropyrimidine aminohydrolase.

The biologically active isomer of 5-fluoro-5,6-dihydrouracil [(R)-5-fluoro-5,6-dihydrouracil, R-FUH2] was synthesized to study the kinetics of its enzymatic oxidation and hydrolysis by homogeneous dihydropyrimidine dehydrogenase (DPDase) and dihydropyrimidine aminohydrolase (DPHase), respectively. DPDase catalyzed the slow oxidation of R-FUH2 at pH 8 and 37 degrees with a Km of 210 microM and a kcat of 0.026 sec-1 at a saturating concentration of NADP+. The catalytic efficiency (kcat/Km) of DPDase for R-FUH2 was 1/14th of that for 5,6-dihydrouracil (UH2). In the opposite direction, DPDase catalyzed the reduction of 5-fluorouracil (FU) with a Km of 0.70 microM and a kcat of 3 sec-1 at a saturating concentration of NADPH. Thus, DPDase catalyzed the reduction of FU 30,000-fold more efficiently than the oxidation of R-FUH2. In contrast to the slow oxidation of R-FUH2 by DPDase, R-FUH2 was hydrolyzed very efficiently by DPHase with a Km of 130 microM and a kcat of 126 sec-1. The catalytic efficiency of DPHase for the hydrolysis of R-FUH2 was approximately twice that for the hydrolysis of UH2. Because R-FUH2 is hydrolysis of R-FUH2 was approximately twice that for the hydrolysis of UH2. Because R-FUH2 is hydrolyzed considerably more efficiently than it is oxidized and because the activity of DPHase was 250- to 500-fold greater than that of DPDase in bovine and rat liver, the hydrolytic pathway should predominate in vivo.

Amidohydrolases↗