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Query: EC:3.1.3.5 (5'-nucleotidase)
 3,167 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The contribution of 5'-nucleotidase and AMP-deaminase to adenine nucleotide degradation in human cardiomyocytes isolated from diseased or normal heart was investigated. The preparation used contained 30 to 50% of viable cells and the nucleotide degradation was stimulated by addition of deoxyglucose and oligomycin. To distinguish pathways of nucleotide degradation, adenosine deaminase was inhibited by erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA). Under these conditions, ATP concentration was decreased by 60% after 45 min of incubation. Simultaneously, increases in intra- and extracellular catabolite concentrations have been observed. Adenosine was the predominant catabolite found in both the cells and in the extracellular medium accounting for more than 70% of all degradation products. Intracellular adenosine concentration rose to 300 times greater than that outside the cell. An increase in intra- and extracellular inosine was also seen. Only a small increase of IMP concentration was observed. No hypoxanthine accumulation was found. No significant change in initial adenine nucleotide concentrations were observed in isolated cells during aerobic incubation without deoxyglucose and oligomycin. In conclusion, a pathway involving adenosine production appears to be the principal route of nucleotide degradation in human cardiomyocytes.
J Mol Cell Cardiol 1992 Jan
PMID:Adenine nucleotide catabolism and adenosine formation in isolated human cardiomyocytes. 156 34

The metabolic fate of labeled hypoxanthine and inosine, degradation products of adenine nucleotides, was studied in cultured beating cardiomyocytes, in order to assess the physiological significance of their contribution to salvage nucleotide synthesis in the heart. Inosine and hypoxanthine were found to be incorporated into nucleotides by a similar rate, but in the presence of 8-aminoguanosine, a potent inhibitor of purine nucleoside phosphorylase (EC 2.4.2.1), the rate of inosine incorporation into nucleotides was markedly reduced (by 75%), indicating that inosine incorporation to IMP (inosinic acid) occurs following its degradation to hypoxanthine. The proportion of hypoxanthine converted to IMP by hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8) is markedly greater than that degraded to xanthine and uric acid by xanthine oxidase (EC 1.3.2.3). However, close to 50% of the IMP formed was degraded to inosine by IMP 5'-nucleotidase (EC 3.1.3.5). The results demonstrate the activity of the following futile cycle in the cardiomyocytes: hypoxanthine----IMP----inosine----hypoxanthine. The rational for the activity of this energy consuming cycle is yet unclear.
J Mol Cell Cardiol 1992 Feb
PMID:Metabolic fate of hypoxanthine and inosine in cultured cardiomyocytes. 158 1

The controversial subject of the subcellular location of myocardial adenosine production was studied employing density gradient fractionation of heart muscle combined with a novel method for analyzing distribution profiles based on multiple regression (correlation) analysis. Bungarotoxin binding, N-acetyl-beta-D-glucosaminidase, cytochrome c oxidase, NADPH-dependent cytochrome c reductase and lactate dehydrogenase were used as markers for the plasma membrane, lysosomes, mitochondria, sarcoplasmic reticulum and cytosol, respectively. The normalized distribution frequencies (fraction of total) of 5'-nucleotidase in mitochondria, lysosomes, plasma membranes, sarcoplasmic reticulum and cytosol in the 50 x g supernatant of total homogenate of heart muscle were found to be 0, 0.25, 0.44, 0.08 and 0.23, respectively. To increase the resolution power of this approach with respect to mitochondria, a crude mitochondrial fraction was also studied, in which the normalized distribution of 5'-nucleotidase in the homogenate was 0, 0.16 and 0.84 in mitochondria, plasma membranes and lysosomes, respectively. This mainly lysosomal 5'-nucleotidase activity was 61% inhibited by the alpha,beta-methylene analog of ADP, indicating that although the latter has been considered specific to the plasma membrane enzyme, it also inhibits the lysosomal enzyme. The intercellular distribution of 5'-nucleotidase was not studied, but the lack of this enzyme in the mitochondria indicate that the adenosine production observed during mitochondrial AMP production, e.g. during acetate oxidation in intact heart muscle, must involve AMP transport out from the mitochondria.
J Mol Cell Cardiol 1990 Jul
PMID:Subcellular distribution of myocardial 5'-nucleotidase. 223 47

Adenosine may modulate blood flow and electrical activity in heart in response to changes in myocardial energy metabolism. In the present study, 31P NMR spectroscopy was used to examine the relation between cytosolic phosphate metabolite levels and release of adenosine into the venous effluent of isovolumic heart during graded low-flow ischaemia or metabolic stimulation with isoproterenol. When coronary flow rate was varied in steps between 1.6 and 12 ml/min/g, cytosolic ATP levels did not change significantly but the phosphorylation potential exhibited a linear correlation with flow rate below approximately 7 ml/min/g. Purine release (adenosine and inosine) correlated linearly with the cytosolic phosphorylation potential and free AMP concentration. Metabolic stimulation of hearts with isoproterenol (0.4, 3.0, and 60 nM), produced a significant fall in cytosolic ATP levels and decreased the cytosolic phosphorylation potential. Purine release in these hearts increased exponentially as the cytosolic phosphorylation potential dropped, and as cytosolic free AMP increased. These results support a link between the phosphorylation potential and the mechanism of adenosine production during ischaemia and metabolic stimulation. Presumably, this link is the activity of the enzyme 5'-nucleotidase, which is responsible for converting AMP to adenosine, together with the concentration of its substrate, AMP. In low-flow ischaemia, cytosolic AMP may control adenosine formation. With isoproterenol stimulation, a more complex relationship exists, indicating possible allosteric regulation of the enzyme(s) responsible for adenosine formation, in addition to changes in AMP concentration.
J Mol Cell Cardiol 1989 Nov
PMID:Adenosine production and energy metabolism in ischaemic and metabolically stimulated rat heart. 255 22

The transmural distribution of the adenosine-generating enzyme 5'-nucleotidase (5'N) and of the adenosine-degrading enzymes adenosine deaminase (ADA), AMP deaminase (AMP-D) and adenosine kinase (Ado-K) were determined across the walls of left and right ventricles of control and hypertrophic rat hearts. The enzyme distribution across the left ventricle wall (but not across the right wall) of normal hearts was not uniform: 5'N activity shows its highest levels in the subepicardial and in the subendocardial regions, whereas all the other enzyme activities show their lowest levels. A similar pattern of transmural distribution was also detected in other mammalian species (ox and pig). In the experimental cardiac hypertrophy, caused by two different types of chronic cardiac overload, the levels and the profiles of transmural distribution of 5'N and ADA enzyme activities may significantly change across the rat left ventricle wall.
Basic Res Cardiol
PMID:The regional distribution of adenosine-regulating enzymes in the left and right ventricle walls of control and hypertrophic heart. 255 11

The activities of the adenosine-generating enzyme 5'-nucleotidase and the adenosine-degrading enzyme adenosine deaminase were determined for four regions of rat hearts prior to and following 10-60 min of ischaemia. Whereas adenosine deaminase was uniformly active throughout the heart, 5'-nucleotidase was twice as active in atrial than in ventricular myocardium, and more active in the right than in the left ventricles in normoxic tissues. In isolated heart preparations normoxic perfusion decreased adenosine deaminase and increased 5'-nucleotidase activity compared to levels in vivo. Global ischaemia for 10 min elevated adenosine deaminase activity but had no effect on 5'-nucleotidase activity. However, 30 min of ischaemia decreased 5'-nucleotidase activity by 50% in all regions of the heart. These changed levels were not altered by 10 min of reperfusion. The fall in 5'-nucleotidase activity with ischaemia occurred only in the 90% of this enzyme which is membrane-bound. The reasons for the marked differences in distribution and responses to ischaemia of these two enzymes have yet to be elucidated but metabolic inhibitors seem unlikely to be involved.
Basic Res Cardiol
PMID:Differences in the regional distribution and response to ischaemia of adenosine-regulating enzymes in the heart. 282 14

The effect of verapamil on sarcolemmal activities of sarcolemmal fragments isolated from aerobically perfused (control) and ischaemic rat hearts was examined. Adding verapamil to the perfusate of aerobically perfused hearts for 75 min enhanced some of the sarcolemmal activities; Na+-K+ ATPase (31%), K+ stimulated phosphatase (31%) and Na+-Ca2+ exchange rate (46%). Adding verapamil directly to the enzymatic incubation media, or to the cardiac homogenate prior to sarcolemmal isolation did not alter these activities, suggesting that these changes are dependent upon addition of verapamil to the intact system. Addition of verapamil to hearts 15 min prior to a 60 min ischaemic episode maintained a number of sarcolemmal activities close to those obtained after aerobic perfusion. Na+-K+ ATPase activity and Na+-Ca2+ exchange received a relative protection while K+ stimulated phosphatase activity was not protected. 5'-nucleotidase activity was completely protected against ischaemia-induced depression. The mechanism whereby verapamil induces these changes in sarcolemmal enzymatic activities is unclear but its ability to maintain these activities at or near normal levels may contribute to its ability to protect against the deleterious effects of ischaemia.
J Mol Cell Cardiol 1985 Jul
PMID:The effect of verapamil on ischaemia-induced changes to the sarcolemma. 299 43

Activities of several adenosine metabolizing enzymes were examined in capillary preparations isolated from rabbit ventricle. Vmax and Km values for 5'-nucleotidase were 2.3 nmol/min/mg and 10 microM, respectively. For adenosine deaminase the corresponding values were 7.8 nmol/min/mg and 32 microM. S-adenosyl-homocysteine hydrolase, which forms adenosine by the hydrolysis of S-adenosylhomo-cysteine, was also present (Vmax, 0.07 nmol/min/mg; Km, 0.81 microM), as were adenosine kinase (Vmax, 0.2 nmol/min/mg; Km, 0.52 microM) and purine nucleoside phosphorylase (Vmax, 13.8 nmol/min/mg; Km, 96 microM). These enzymes were also present in microvessels (capillaries and arterioles) purified from rabbit brain. Activities of several enzymes, especially 5'-nucleotidase and adenosine deaminase, were much lower in myocytes isolated from rabbit ventricle. The study provides evidence that endothelial cells of the microvasculature from heart and brain are capable of activity forming and degrading adenosine. It is possible that adenosine formed by these cells may contribute to the local regulation of blood flow.
J Mol Cell Cardiol 1986 Jan
PMID:Adenosine metabolism in microvessels from heart and brain. 300 95

We have examined adenosine (ADO) production and transport in a preparation of isolated adult cardiocytes which attach to and form a monolayer on culture dishes. This preparation contains 85% viable cells which are greater than 50% rod shaped and maintain an ATP/ADP ratio of nine. Incubation under control conditions for 15 mins results in a net release of 240 +/- 47 pmol ADO/mg protein (final adenosine concentration in the medium = 47 +/- 9 nM). Both 0.1 mM dinitrophenol (DNP) and 10 mM iodoacetate (IAA) cause a significant increase in ADO (DNP = 1763 +/- 147 and IAA = 612 +/- 90 pmol/mg). Both 20 microM nitrobenzylthioinosine (NBMPR), an inhibitor of the purine nucleoside carrier, and 0.1 mM alpha,beta-methylene adenosine diphosphate (AOPCP), an inhibitor of 5'-nucleotidase activity, attenuate DNP-stimulated ADO release (NBMPR by 62% and ADOCP by 76%). The results are consistent with the hypothesis that under the conditions of our experiments, adenosine is formed by a 5'-nucleotidase in association with transport across the cell membrane, perhaps by an enzyme-carrier complex. In addition, we have examined the effect of 0.1 mM dipyridamole on the extracellular appearance of adenosine in this preparation and found that it causes a significant increase in the amount of adenosine released. These results are consistent with the hypothesis that dipyridamole inhibits adenosine's uptake more than its release in cardiac myocytes.
J Mol Cell Cardiol 1986 Jun
PMID:Adenosine production and release by adult rat cardiocytes. 301 89

The subcellular distribution of the 5'-nucleotidase activity was investigated in normal and hypertrophied pig hearts; normal rat hearts were used for comparison. The left ventricular hypertrophy was induced in pigs by banding the supravalvular aorta for 4, 8 and 12 weeks. By employing different procedures for the isolation of cardiac membranes, a major catalytic site for 5'-nucleotidase was found to be located at sarcolemma in rat heart and microsomes (sarcoplasmic reticulum) in pig heart. A progressive decrease in the homogenate and microsomal 5'-nucleotidase activity occurred upon the development of myocardial hypertrophy in pigs. This reduction in microsomal 5'-nucleotidase activity was characterized by a depression in both apparent Vmax and Km values. These results indicate that a primary 5'-nucleotidase pool is present in the intracellular compartment of the pig heart and is altered during the development of hypertrophy.
J Mol Cell Cardiol 1986 Aug
PMID:Subcellular distribution of cardiac 5'-nucleotidase: alteration of microsomal pool in hypertrophied pig heart. 301 68


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