5′-Nucleotidases in rat heart. Evidence for the occurrence of two soluble enzymes with different substrate specificities

Truong, V L; Collinson, Albert R.; Lowenstein, John M.

doi:10.1042/bj2530117

Cited by 93 publications

(63 citation statements)

References 17 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The /'¿'..-valúes for both substrates were 2-4 times higher in human heart 1), a lower affinity of 5'-NT for AM P and IM P in man. Our results in rat heart were comparable with those from Truong et al [35]. We found a 13-fold lower initial concentration of inosine accumulated in freshly prepared human-heart supernatant fluids compared to rat-heart ones.…”

Section: '-Nucleotidasesupporting

confidence: 82%

Kinetics of adenylate metabolism in human and rat myocardium

Tavenier

Składanowski

Abreu

et al. 1995

Biochimica et Biophysica Acta (BBA) - General Subjects

View full text Add to dashboard Cite

A bstractPathways producing and converting adenosine have hardly been investigated in human heart, contrasting work in other species. We compared the kinetics of enzymes associated with purine degradation and salvage in human and rat heart cytoplasm assaying for adenosine deaminase, nucleoside phosphorylase, xanthine oxidoreductase, AMP deaminase, AMP-and IMP-specific 5'-nucleotidases, adenosine kinase and hypoxanthine guanine phosphoribosyltransferase (HGPRT). Xanthine oxidoreductase was not detectable in human heart. The /Tm-values of the AMP-catabolizing enzymes were 2-5 times higher in human heart; the substrate affinity of the other enzymes was in the same order of magnitude in both species. The maximal activity (Vmax) of adenosine kinase was the same in both species, but HGPRT in man was only 12% of that in the rat. For human heart the VLax-values of adenosine deaminase, nucleoside phosphorylase, AMP-and IMP-specific 5'-nucleotidases, and AMP deaminase were 25-50% of those for rat heart. We conclude that human heart is less geared to purine catabolism than rat heart as is evident from the lower activities of the catabolic enzymes. Maintenance of the nucleotide pool may thus play a more important role in human heart.

show abstract

Section: '-Nucleotidasesupporting

confidence: 82%

Kinetics of adenylate metabolism in human and rat myocardium

Tavenier

Składanowski

Abreu

et al. 1995

Biochimica et Biophysica Acta (BBA) - General Subjects

View full text Add to dashboard Cite

show abstract

“…There are in fact two known forms of 5'-nucleotidase: one is membrane bound (ecto-5'-nucleotidase) and the other is a free or soluble form found in the cytoplasm (cytosolic 5'_nucleotidase). Ecto-5'-nucleotidase has a lower Km for AMP (•20 ìÒ) than does cytosolic 5'-nucleotidase (•3 mÒ) (Sullivan & Alpers, 1971;Truong, Collinson & Lowenstein, 1988). In the present study the AMP-induced increases in the dialysate adenosine concentration depended on the AMP concentration, and the AMP concentration for the halfmaximal effect of adenosine production (EC50) was 116·1 ìÒ (Fig.…”

Section: Discussionmentioning

confidence: 63%

Stimulation of α₁‐adrenoceptors and Protein Kinase C‐mediated Activation of Ecto‐5′‐Nucleotidase in Rat Hearts in vivo

Sato

Obata

Yamanaka

et al. 1997

The Journal of Physiology

View full text Add to dashboard Cite

To determine whether protein kinase C (PKC)‐mediated activation of ecto‐5′‐nucleotidase would increase interstitial adenosine concentrations in the rat heart in vivo, we made use of the microdialysis technique and a flexibly mounted probe, which was implanted in the left ventricular myocardium and perfused with Tyrode solution. The baseline level of dialysate adenosine was 0.51 ± 0.09 μM (n= 16). Perfusion of adenosine 5′‐monophosphate (AMP, 100 μM) through the probe increased the dialysate adenosine concentration markedly to 9.25 ± 0.46μM (n= 15). αβ‐Methyleneadenosine 5′‐diphosphate (AOPCP, 100 μM), an inhibitor of ecto‐5′‐nucleotidase, abolished the AMP‐induced increase in dialysate adenosine, but did not affect the baseline level of adenosine. These observations suggest that the dialysate adenosine obtained during the perfusion with AMP, but not the baseline levels of adenosine, originated from the dephosphorylation of AMP by ecto‐5′‐nucleotidase. Thus, the level of adenosine measured during AMP perfusion gives an index of the activity of ecto‐5′‐nucleotidase in the tissue. Noradrenaline (10 μm) increased the adenosine concentration measured in the presence of 100 μm AMP (i.e. the activity of ecto‐5′‐nucleotidase) by 38.7 ± 9.6 % (n= 5, P < 0.05), an increase which was inhibited by an antagonist of the α1adrenoceptor (prazosin, 50 μM) or of PKC (chelerythrine, 10 μm). Further application of either the α1‐adrenoceptor agonist methoxamine (100 μM) or the diacylglycerol analogue 1,2‐dioctanoyl‐sw‐glycerol (DOG, 100 μm) also increased the adenosine concentration by 35.1 ± 10.0% (n= 6, P < 0.05) or 40.6 ± 8.3% (n= 5, P < 0.05), respectively. The presence of okadaic acid (50 μm), an inhibitor of protein phosphatase, enhanced the noradrenaline‐induced increase in adenosine concentration by 112.4 ± 35.9% (n= 4, P < 0.05), to a level significantly (P < 0.05) greater than the increase caused by noradrenaline alone (38.7 ± 9.6%). These data provide the first evidence that α1‐adrenoceptor stimulation and the subsequent activation of PKC can increase adenosine concentrations in interstitial spaces of ventricular muscle in vivo, through activation of endogenous ecto‐5′‐nucleotidase.

show abstract

“…In rat heart, control ADP concentrations of 64 M increase to 106 M under hypoxic conditions (32). These fluctuations in ADP levels are precisely within the range of A 0.5 value for this activator and further signify the important role of this enzyme in adenosine generation in the heart during ischemia (15,17,24) and potentially also in working skeletal muscle. Interestingly, recombinant human cN-I is also significantly activated by GTP, and an increase in GTP levels, for example during cellular proliferation, may also play a role in activation of the enzyme.…”

Section: Discussionmentioning

confidence: 89%

“…The kinetic characteristics of cN-I and cN-II have been studied to determine the contribution of each enzyme to this process. From the characteristics of the purified cN-I enzyme and the cloned pigeon cN-I enzyme, cN-I has been identified as the enzyme responsible for most of the adenosine production in hypoxic and ischemic heart tissue (15,19,24,30). Although cN-I has been purified and characterized from rabbit, rat, pigeon, dog, and human hearts, there is only limited information on its role in pyrimidine metabolism (17,20).…”

Section: Discussionmentioning

confidence: 99%

Human Cytosolic 5′-Nucleotidase I

Hunsucker

Spychała

Mitchell

2001

Journal of Biological Chemistry

View full text Add to dashboard Cite

Nucleoside analogs are important in the treatment of hematologic malignancies, solid tumors, and viral infections. Their metabolism to the triphosphate form is central to their chemotherapeutic efficacy. Although the nucleoside kinases responsible for the phosphorylation of these compounds have been well described, the nucleotidases that may mediate drug resistance through dephosphorylation remain obscure. We have cloned and characterized a novel human cytosolic 5-nucleotidase ( Nucleoside analogs are used as chemotherapeutic agents in the treatment of hematologic malignancies and as anti-viral drugs. These compounds are taken up by cells through nucleoside transporters in the cell membrane or, in the case of more lipophilic drugs, through diffusion (1-3). Once in the cytoplasm, the nucleoside analogs are substrates for phosphorylation by the nucleoside kinases of the deoxyribonucleoside salvage pathway (reviewed in Ref. 4). The enzyme 2Ј-deoxycytidine kinase phosphorylates dAdo, dCyd, and dGuo as well as the analogs AraC, 1 dFdC, and CdA, whereas thymidine kinase 1 phosphorylates dThd and dUrd as well as the analogs d4T and 5-FU. Phosphorylation to the monophosphate form is considered the rate-limiting step of activation of nucleoside analogs (4). Nucleoside analog monophosphates are rapidly phosphorylated to their triphosphate forms, which are believed to mediate their cytotoxic activities by several different mechanisms (reviewed in Ref. 5). For example, they can be directly incorporated into DNA, leading to chain termination, or they can inhibit DNA synthesis by direct inhibition of DNA polymerase. It has recently been demonstrated that certain of these metabolites, including CdATP, AraATP, and F-AraATP, can induce apoptosis in nonproliferating cells by interacting with cytochrome c and apoptosis protein-activating factor-1 (APAF-1) to cleave and activate the caspases responsible for the induction of apoptosis (6, 7). In contrast, the triphosphates of antiretroviral compounds, such as 2Ј,3Ј-dideoxycytidine (ddC) and d4T, inhibit the reverse transcriptase of the human immunodeficiency virus through chain termination. Cytotoxicity can occur when these compounds are incorporated into nuclear or mitochondrial DNA (reviewed in Ref. 8).Resistance to nucleoside analogs is a significant clinical problem and can be caused by a number of factors affecting the metabolism of the drugs, including decreased numbers of nucleoside transporters, increased deamination of cytidine and adenosine analogs, loss of expression of activating kinases, modulation of the downstream apoptotic machinery, and increased activity of nucleotidases that catalyze the conversion of nucleotides back to nucleosides (reviewed in Ref. 5). The 5Ј-nucleotidases oppose the action of nucleoside kinases by dephosphorylating the monophosphate form of nucleosides and nucleoside analogs and, therefore, are likely to be important in determining the sizes and turnover rates of the deoxyribonucleotide pools. Thus, 5Ј-nucleotidases that catabolize the monophos...

show abstract

5′-Nucleotidases in rat heart. Evidence for the occurrence of two soluble enzymes with different substrate specificities

Cited by 93 publications

References 17 publications

Kinetics of adenylate metabolism in human and rat myocardium

Kinetics of adenylate metabolism in human and rat myocardium

Stimulation of α₁‐adrenoceptors and Protein Kinase C‐mediated Activation of Ecto‐5′‐Nucleotidase in Rat Hearts in vivo

Human Cytosolic 5′-Nucleotidase I

Contact Info

Product

Resources

About

5′-Nucleotidases in rat heart. Evidence for the occurrence of two soluble enzymes with different substrate specificities

Cited by 93 publications

References 17 publications

Kinetics of adenylate metabolism in human and rat myocardium

Kinetics of adenylate metabolism in human and rat myocardium

Stimulation of α1‐adrenoceptors and Protein Kinase C‐mediated Activation of Ecto‐5′‐Nucleotidase in Rat Hearts in vivo

Human Cytosolic 5′-Nucleotidase I

Contact Info

Product

Resources

About

Stimulation of α₁‐adrenoceptors and Protein Kinase C‐mediated Activation of Ecto‐5′‐Nucleotidase in Rat Hearts in vivo