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O Sperling

Publications and source records attributed to O Sperling.

At least 19 recordsLinked to original sources
PubMed1995

Metabolism of guanine and guanine nucleotides in primary rat cardiomyocyte cultures.

The metabolic fate of labeled guanine and of prelabeled guanine nucleotides (GuRN) was studied in cultured rat cardiomyocytes. Special attention was given to guanine salvage in comparison to degradation; to the contribution of GuRN to adenine nucleotides (AdRN); to the fluxes from GMP to IMP and from IMP to GMP; and to the degradation pathways of GuRN. In accordance with the 3- to 4-fold higher activity of guanine deaminase (guanase), in comparison to that of hypoxanthine-guanine phosphoribosyltransferase (HGPRT), the rate of guanine deamination to xanthine exceeded that of guanine incorporation into nucleotides (at 4 microM) by 13.2-fold. The label from guanine incorporated into nucleotides was found mainly (81%) in GuRN, but also in IMP and AdRN. The prelabeled GuRN lost 43% of the label in 4 h, reflecting mainly degradation to xanthine (and uric acid) and synthesis of nucleic acids. Blocking nucleoside degradation was associated with a marked accumulation of label in guanosine and inosine (guanosine/inosine labeling ratio is 1.25). The results indicate that in the myocardium guanine is a poor substrate for salvage synthesis of GuRN and that its contribution to the homeostasis of adenine nucleotides is negligible; that GMP degradation to xanthine proceeds through both guanosine and IMP; and that the cardiomyocytes contain the activity of GMP reductase and of the enzymes converting IMP to GMP.

Animals↗
PubMed1995

Role of cellular ribose-5-phosphate content in the regulation of 5-phosphoribosyl-1-pyrophosphate and de novo purine synthesis in a human hepatoma cell line.

5-Phosphoribosyl-1-pyrophosphate (PRPP) is an important regulator of de novo purine synthesis. However, the role of ribose-5-phosphate (R5P), the precursor for PRPP, in the regulation of PRPP and de novo purine synthesis has not yet been clarified conclusively. This study was designed to clarify interrelationships between R5P content, PRPP availability, and the rate of de novo purine synthesis in the cultured human hepatoma cell line (HepG2), a plausible model for normal human hepatocytes. Increasing glucose concentration in the culture media from 0 to 10 mmol/L resulted in a 2.9-fold elevation of cellular R5P content (from 107 +/- 31 to 311 +/- 57 nmol/g protein), associated with a correlated increase of 7.14-fold in cellular PRPP availability (from 4.76 +/- 3.4 to 34 +/- 8.4 pmol/mg protein/min) and of 149-fold in the rate of de novo purine synthesis (from 55 to 8,204 dpm/mg protein/h). Plotting the rate of de novo purine synthesis versus R5P content indicates that at a wide range of R5P content, including that prevailing in hepatocytes under physiological conditions, the rate of purine synthesis depends on R5P content. A similar dependence was also demonstrated for PRPP availability. The rate of de novo purine synthesis exhibited a sigmoidal dependence on PRPP availability. The demonstration in human hepatocytes of dependence of the rate of purine synthesis on R5P content has implications concerning the pathogenesis of purine overproduction associated with several inborn and acquired conditions in man.

Carcinoma, Hepatocellular↗
PubMed1992

Metabolic fate of hypoxanthine and inosine in cultured cardiomyocytes.

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.

Cells, Cultured↗
PubMed1992

Metabolism of guanine and guanine nucleotides in primary rat neuronal cultures.

The metabolic fate of guanine and of guanine ribonucleotides (GuRNs) in cultured rat neurons was studied using labeled guanine. 8-Aminoguanosine (8-AGuo), an inhibitor of purine nucleoside phosphorylase, was used to clarify the pathways of GMP degradation, and mycophenolic acid, an inhibitor of IMP dehydrogenase, was used to assess the flux from IMP to GMP and, indirectly, the activity of the guanine nucleotide cycle (GMP----IMP----XMP----GMP). The main metabolic fate of guanine in the neurons was deamination to xanthine, but significant incorporation of guanine into GuRNs, at a rate of approximately 8.5-13.1% of that of the deamination, was also demonstrated. The turnover rate of GuRNs was fast (loss of 80% of the radioactivity of the prelabeled pool in 22 h), reflecting synthesis of nucleic acids (32.8% of the loss in radioactivity) and degradation to xanthine, guanine, hypoxanthine, guanosine, and inosine (49.3, 4.3, 4.1, 1.1, and 0.5% of the loss, respectively). Of the radioactivity in GuRNs, 7.9% was shifted to adenine nucleotides. The accumulation of label in xanthine indicates (in the absence of xanthine oxidase) that the main degradative pathway from GMP is that to xanthine through guanosine and guanine. The use of 8-AGuo confirmed this pathway but indicated the operation of an additional, relatively slower degradative pathway, that from GMP through IMP to inosine and hypoxanthine. Hypoxanthine was incorporated mainly into adenine nucleotide (91.5%), but a significant proportion (6%) was found in GuRNs.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Stimulation of ribose-5-phosphate and 5-phosphoribosyl-1-pyrophosphate generation by pyrroline-5-carboxylate in mouse liver in vivo: evidence for a regulatory role of ribose-5-phosphate availability in nucleotide synthesis.

Pyrroline-5-carboxylase (P5C), a physiological stimulator of hexose-monophosphate-pentose pathway activity, was found before to increase 5-phosphoribosyl-1-pyrophosphate (PRPP) generation and nucleotide synthesis in human erythrocytes and cultured fibroblasts. We now report the stimulation of PRPP generation by P5C also in mouse liver in vivo. In addition we demonstrated a simultaneous elevation in ribose-5-phosphate (R5P) concentration, which was relatively smaller and transient. The demonstrated effect of P5C on liver R5P and PRPP content in vivo provides strong evidence for the physiological role of R5P availability in the regulation of PRPP and purine production.

Animals↗
PubMed1991

Acceleration of purine synthesis in mouse liver by glycogenolytic hormones.

Administration (ip) into fed mice of glucagon, epinephrine, vasopressin, oxytocin, angiotensin II, and dibutyryl cyclic AMP (dbcAMP) resulted in a rapid (within 2.5 to 15 min) elevation of PRPP content (two- to threefold) and in acceleration of the rate of de novo purine synthesis (twofold). Inhibition of the epinephrine-stimulated glycogenolysis by 2,5-anhydromannitol diminished markedly the acceleration effect of the hormone on the rate of purine synthesis. Administration of the hormones caused a rapid rise in the liver content of glucose 6-phosphate (G6P) by 15-70% but did not increase the ribose 5-phosphate (R5P) content. Liver ATP content was not affected. The hormones did not cause direct activation of PRPP synthetase, as gauged by the specific activity of the enzyme, its Km for substrates R5P and ATP, and its sensitivity to inhibition by ADP and GDP. The hormones did not increase the liver content of the enzyme activators Pi and Mg2+. The results suggest that the glycogenolytic hormones accelerate purine synthesis by a metabolic mechanism associated with the enhancement of glycogenolysis. PRPP synthesis is probably enhanced by the glycogenolysis-induced alterations in the cellular content of some metabolites other than R5P.

Animals↗
PubMed1990

Developmental changes in the activity of enzymes of purine metabolism in rat neuronal cells in culture and in whole brain.

The activities (Vmax) of several enzymes of purine nucleotide metabolism were assayed in premature and mature primary rat neuronal cultures and in whole rat brains. In the neuronal cultures, representing 90% pure neurons, maturation (up to 14 days in culture) resulted in an increase in the activities of guanine deaminase (guanase), purine-nucleoside phosphorylase (PNP), IMP 5'-nucleotidase, adenine phosphoribosyltransferase (APRT), and AMP deaminase, but in no change in the activities of hypoxanthine-guanine phosphoribosyltransferase (HGPRT), adenosine deaminase, adenosine kinase, and AMP 5'-nucleotidase. In whole brains in vivo, maturation (from 18 days of gestation to 14 days post partum) was associated with an increase in the activities of guanase, PNP, IMP 5'-nucleotidase, AMP deaminase, and HGPRT, a decrease in the activities of adenosine deaminase and IMP dehydrogenase, and no change in the activities of APRT, AMP 5'-nucleotidase, and adenosine kinase. The profound changes in purine metabolism, which occur with maturation of the neuronal cells in primary cultures in vitro and in whole brains in vivo, create an advantage for AMP degradation by deamination, rather than by dephosphorylation, and for guanine degradation to xanthine over its reutilization for synthesis of GMP. The physiological meaning of the maturational increase in these two ammonia-producing enzymes in the brain is not yet clear. The striking similarity in the alterations of enzyme activities in the two systems indicates that the primary culture system may serve as an appropriate model for the study of purine metabolism in brain.

Adenosine Monophosphate↗
PubMed1989

Thyroxine-induced redistribution of creatine kinase isoenzymes in rat cardiomyocyte cultures.

The present study demonstrates a change occurring in the creatine-kinase isoenzyme profile of cardiomyocyte cultures induced by a chronic administration of excessive amounts of thyroid hormones (TH). This change is manifested by an increased level of the CK-BB isoenzyme, generally at the expense of CK-MM isoenzyme. The elevation of CK-BB is probably a result of a specific effect of TH through activation of gene expression, rather than a contribution of an increased number of non-myocardial cells. The implications of these results in the diagnosis of heart failures are discussed.

Animals↗
PubMed1989

Prenatal diagnosis of Lesch-Nyhan syndrome: experience with three fetuses at risk.

Our experience with the prenatal detection of the Lesch-Nyhan syndrome (LNS; hypoxanthine-guanine phosphoribosyltransferase (HGPRT) deficiency) in three fetuses at risk is reported. Enzyme activities were measured in cultured amniocytes in two pregnancies, and in tissues and cultures obtained from chorionic villus sampling (CVS) in a third pregnancy. In all tissues the specific activities of HGPRT and adenine phosphoribosyltransferase (APRT) were determined and APRT/HGPRT ratios were calculated. In addition to the enzyme assays, the rate of purine synthesis de novo was assessed in the two amniocyte cultures, and the rate of [14C]hypoxanthine incorporation into nucleotides and sensitivity to azaguanine were measured in one of the amniocyte cultures. We report the diagnosis of normal fetuses by study of amniocytes in two pregnancies and of LNS using CVS in one pregnancy. In all three cases the diagnosis was confirmed.

Adenine Phosphoribosyltransferase↗
PubMed1989

Guanine ribonucleotide metabolism in human red blood cells: evidence for a high rate of GMP dephosphorylation.

The flux rates through the metabolic pathways affecting the maintenance of GuRN pool in intact human RBC were studied. Normal RBC, incubated in KRBB, exhibited a markedly higher accumulation in nucleotides of Gu than of Hx. Addition of 8-AGuo, a potent inhibitor of PNP, resulted in a marked increase in the accumulation of label in the nucleosides, in Ino following incubation with Hx, and in Guo following incubation with Gu, indicating a very high rate of IMP and GMP degradation to bases through their respective nucleosides. Most of the degradation of GMP is by dephosphorylation to Guo, rather than through reductive deamination to IMP. The ultimate fate of IMP in RBC is its degradation to Ino and consequently to Hx. The contribution of AdRN or of IMP to the GuRN pool is negligible. The results indicate that concerning IMP and GMP, human RBC contain very active futile cycles, nucleotide----nucleoside----base----nucleotide, catalyzed by 5'-nucleotidase, PNP, and HGPRT. The operation of the complete cycles is essential for the maintenance of GuRN and the IMP pool size. These results may explain the finding of reduced GTP content in RBC from patients with an inborn deficiency of PNP or of HGPRT.

Erythrocytes↗
PubMed1989

Does determination of serum aspartate aminotransferase contribute to the diagnosis of acute myocardial infarction?

Values for total lactate dehydrogenase (LD), LD isoenzymes, and serum aspartate aminotransferase (AST) were determined in 150 patients with acute myocardial infarction (AMI) and 130 non-AMI patients 24, 48, and 72 hours after admission. The authors assessed the diagnostic yield of a single determination of AST, LD, and three LD isoenzymes tests: LD-1 greater than LD-2; LD-1 greater than 90 U/L; LD-1/LD greater than 0.4. They also assessed the diagnostic accuracy of combined determination of AST with LD and AST with each of the above three LD isoenzymes tests. The efficiency of single determination of AST was better than that of LD (88% vs. 80%, 48 hours after admission). The most efficient single test for diagnosing AMI was the LD-1 greater than 90 U/L test (92%, 48 hours after admission). The efficiency of the combined AST/LD test was better than that of a single determination of each of the two enzymes (90% vs. 88% and 80%, 48 hours after admission). The highest efficiency was achieved, however, with combined determination of AST and any of the three LD isoenzymes tests. It was found to be more efficient than single determination of each of the LD isoenzymes tests (95.5-96% vs. 89-92.5%) and more efficient than the combined determination of the AST/LD test (95.5-96% vs. 89-90%). The authors conclude that AST should be determined in every patient with suspected AMI because its determination may contribute to the diagnostic yield of LD isoenzymes tests, especially in patients with AMI admitted 48-72 hours after onset of symptoms, when creatine kinase declined to near normal values.

Adult↗