Purine Deoxyribonucleosides Research Articles

Determination of ribonucleosides, deoxyribonucleosides, and purine and pyrimidine bases in adult rabbit cerebrospinal fluid and plasma.

Purine and pyrimidine base and nucleoside levels were measured in adult rabbit cisternal CSF and plasma by reversed-phase high-performance liquid chromatography. The concentrations of bases, nucleosides, and nucleoside phosphates were similar in plasma and CSF except for the adenosine phosphates and uracil which were higher in the plasma. In plasma and CSF, adenosine levels were low (0.12 microM) and guanosine, deoxyadenosine, deoxyguanosine, and deoxyinosine were not detectable (less than 0.1 microM); inosine and xanthine concentrations were 1-2 microM and hypoxanthine concentrations were approximately 5 microM; uridine (approximately 8 microM), cytidine (2-3 microM), and thymidine, deoxyuridine, and deoxycytidine (0.5-1.4 microM) were easily detectable. In both plasma and CSF, guanine, and thymine were undetectable (less than 0.1 microM), adenine and cytosine were less than 0.2 microM, but uracil was present (greater than 1 microM). Adenosine, inosine, and guanosine phosphates were also detectable at low concentrations in CSF and plasma. These results are consistent with the hypothesis that purine deoxyribonucleosides are synthesized in situ in the adult rabbit brain. In contrast, pyrimidine deoxyribonucleosides and ribonucleosides, and purine and pyrimidine bases are available in the CSF for use by the brain.

Formation of 3-(2′-deoxyribofuranosyl) and 9-(2′-deoxyribofuranosyl) nucleosides of 8-substituted purines by nucleoside deoxyribosyltransferase

Earlier results suggested that although the N-deoxyribosyltransferase from lactobacilli is a convenient tool for the preparation of analogs of 2′-deoxyadenosine, 8substituted purines do not act as substrates. However, eight of nine 8-substituted purines that were examined proved to be substrates for the transferase from Lactobacillus leichmannii, and deoxyribonucleosides of four of these bases have been prepared. The substituents at C-8 of the purine greatly affect the rate of deoxyribosyl transfer to the base, and in all cases the rate is slower than transfer to purines lacking an 8-substituent. The 8-substituent also affects the nature of the nucleoside formed. With the electron-donating methyl group at position 8 of adenine, the transferase forms the expected 8-methyl-9-(2′-deoxyribofuranosyl)adenine. However, when purines bearing an electron-withdrawing substituent at the 8-position are used as substrates, the deoxyribosyl moiety is preferentially transferred to N-3 of the base. In the case of 8trifluoromethyladenine the 3-deoxyribonucleoside is the only product detectable. With 8-bromo or 8-chloroadenine as substrate the 3 and 9-deoxyribonucleosides can both be isolated from the enzymatic reaction mixture. Time course studies indicated that with thymidine and 8-bromoadenine as substrates the 3-deoxyribonucleoside is initially the major product, but that the 9-deoxyribonucleoside becomes the major product after long incubation periods. Negligible interconversion of these nucleosides occurs in the absence of transferase, but conversion in either direction occurs readily in the presence of the enzyme. Significant hydrolysis of pyrimidine and purine deoxyribonucleosides occurs in the presence of the transferase. This was more obvious during the course of reactions involving 8-substituted purines because the slowness of deoxyribosyl transfer required longer incubation periods and larger amounts of enzyme. The hydrolysis is proportional to enzyme concentration, little affected by the nature of the base and is attributed to hydrolysis of a deoxyribosyl derivative of the transferase which is an obligatory intermediate of deoxyribosyl transfer. 8-Trifluoromethyl-3-(2′-deoxyribofuranosyl) adenine, 8-methyl-9-(2′-deoxyribofuranosyl)adenine, and 8-bromo-9-(2′-deoxyribofuranosyl) adenine were tested for their ability to inhibit the growth of CCRFCEM cells in culture. Unlike the potent 2-halogeno-2′-deoxyadenosine derivatives, these three nucleosides cause less than 50% inhibition at concentrations up to 100 μ m.

Changes in ribo- and deoxyribonucleoside triphosphate pools within the cell cycle of a synchronized moused fibroblast cell line

Intracellular pool levels of ribo- and deoxyribonucleoside triphosphates were monitored throughout the cell cycle of C3H10T1/2 mouse embryo fibrolast cells synchronized by isoleucine deprivation. Absolute pool sizes of ribonucleoside triphosphates were approximately 30 fold greater than those of the corresponding deoxyribonucleoside triphosphates. Of the ribonucleoside triphosphates, pool sizes of ATP exhibited the greatest change, increasing from a low of 32.7 nmol/10 7 cells during G 1 to a high of 81.6 nmol/10 7 cells 2 h prior to mid S-phase. Levels of ATP subsequently declined to 40.2 nmol/10 7 cells during late S-phase, followed by a second peak of 65.8 nmol/10 7 with the onset of cell division. No significant changes in the pool sizes of UTP and GTP were found throughout the cell cycle. Of the deoxyribonucleoside triphosphates, pool sizes of pyrimidine deoxyribonucleoside triphosphates were approx. 5–10 fold greater than those of purine deoxyribonucleoside triphosphates. Low levels of deoxyribonucleoside triphosphates during G 1 (0.3–1.3 pmol/10 7 cells) increased coordinately with the initiation of DNA synthesis to an initial peak during mid S-phase (0.5–6.4 pmol/10 7 cells). Decling levels of deoxyribonucleoside triphosphates during late S-phase were followed by a subsequent larger second peak (1.7–10.7 pmol/10 7 cells) during G 2-M.

Synthesis of benzyl and benzyloxycarbonyl base-blocked 2'-deoxyribonucleosides

Acylimidazoles have been alkylated with trialkyloxonium tetrafluoroborates to form acylimidazolium salts. These salts, particularly (benzyloxycarbonly)imidazolium salts, are shown to be effective agents for the direct, mono-N-protection of deoxynucleosides as their acyl derivatives. These acyl nucleosides are also available via thiocarbamate intermediates. Thus 3',5'-bis(tert-butyldimethylsilyl)-2'-deoxyguanosine, on treatment with phenyl chlorothioformate, gave the 6-thiophenyl-substituted purine (1). The thiophenyl group of (1) can be replaced by hydrogen, amino, and alkoxy groups to give a variety of substituted purine deoxyribonucleosides.

Reversion of bacteriophage T4rII mutants by high levels of pyrimidine deoxyribonucleosides.

High levels of pyrimidine deoxyribonucleosides, but not purine deoxyribonucleosides, increase the reversion rate of bacteriophage T4rII mutants to r+. This increased reversion rate is not observed when a thymidine kinase mutation is introduced into the bacteriophage, but the high reversion rate persists when the host, E. coli, harbors a thymidine kinase mutation.

Incorporation of deoxyribonucleosides into DNA of coryneform bacteria and the relevance of deoxyribonucleoside kinases.

In order to obtain basic knowledge of the salvage pathways for DNA synthesis, the ability of Brevibacterium ammoniagenes ATCC 6872 and Micrococcus luteus ATCC 15932 for incorporation of nucleobases and nucleosides was investigated. Only adenine and uracil are incorporated by B. ammoniagenes, whereas M. luteus additionally can utilize deoxyadenosine and, less efficiently, thymidine. In M. luteus, the demonstration of deoxyadenosine kinase and thymidine kinase explains the incorporation data. Uptake of thymidine is of short duration because of rapid breakdown of exogenously supplied thymidine to thymine. At a 540-fold excess pyrimidine deoxyribonucleosides inhibit 14C incorporation from thymidine nearly totally and purine deoxyribonucleosides cut by half the uptake rate, probably by interfering with transport of thymidine. However, as no cessation of thymidine incorporation occurs at these concentrations of purine deoxyribonucleosides, incorporation is finally enhanced. During the initial period of this reduced uptake considerable protection of thymidine from breakdown to thymine is provided by deoxyguanosine, but not by deoxyadenosine. At a 108-fold excess there is actually no inhibition of thymidine uptake by deoxyguanosine and only an insignificant impairment by deoxyadenosine resulting in an ultimate enhancement of 14C incorporation up to 20% of the exogenously supplied thymidine. As there is no salvage pathway for thymidine in B. ammoniagenes due to the absence of thymidine kinase, labelling with adenine and hydrolyzing of the 'contaminated' RNA fraction with 1 M KOH is recommended for measurements of overall DNA synthesis in this strain.

Isotope-dilution analysis of the effects of deoxyguanosine and deoxyadenosine on the incorporation of thymidine and deoxycytidine by hydroxyurea-treated thymus cells.

It is presumed that the dGTP and dATP needed for replicative DNA synthesis can be formed by way of either ;salvage' pathways or biosynthesis de novo. This was examined by adding hydroxyurea to cultures of rat thymus cells to inhibit ribonucleoside diphosphate reductase, a key enzyme of the ;de novo' pathway. Most of the inhibition of the incorporation of [Me-(3)H]thymidine and deoxy[5-(3)H]cytidine by low concentrations of hydroxyurea (100-500mum) was prevented by substrates of the salvage pathway (400mum-deoxyguanosine and, to a lesser extent, 200mum-deoxyadenosine). However, isotope-dilution studies indicated that the purine deoxyribonucleosides prevented inhibition by decreasing pyrimidine deoxyribonucleotide competitor pools. Evidence was obtained that a hydroxyurea-induced increase in the thymidine-competitor pool (probably dTTP) was prevented to an equal extent by deoxyguanosine and by the inhibitor of thymidylate synthase, deoxy-5-fluorouridine. These compounds had almost identical effects on hydroxyurea dose-response curves and on thymidine isotope-dilution plots. The evidence suggests that exogenous purine deoxyribonucleosides cannot prevent the inhibition by hydroxyurea of thymus-cell DNA synthesis. This could mean that, with respect to the metabolism of purine deoxyribonucleotides, ribonucleoside diphosphate reductase is tightly coupled to DNA polymerase in a multienzyme complex. The complex would not permit entry of exogenous metabolic intermediates into the ;de novo' pathway, but would still be subject to the regulatory effects of these intermediates. Thus dGTP and dATP formed from exogenous purine deoxyribonucleosides by salvage pathways might deplete pyrimidine deoxyribonucleotide competitor pools by inhibiting relatively hydroxyurea-insensitive activities of ribonucleoside diphosphate reductase.

Stimulation of DNA synthesis and pyrimidine deoxyribonucleoside transport systems in mouse glioma and mouse neuroblastoma cells by inorganic mercury

Biochemical studies on effects of methylmercury and inorganic mercury on mouse glioma and neuroblastoma cells were carried out. Inorganic mercury accelerated DNA synthesis of mouse glioma cells at 10 −6 to 10 −5 m specifically in the middle log phase of the growth. Inorganic mercury facilitated the thymidine and deoxycytidine transports within a narrow range of concentration (1 to 2 × 10 −5 m), but no stimulation of transport was observed in the cases of purine deoxyribonucleosides. Inorganic mercury markedly inhibited both DNA synthesis and the transport systems of the precursors above 5 × 10 −5 m. On the other hand, methylmercury showed hardly any accelerating effects and markedly inhibited both the synthesis of DNA and the precursors' transport above 5 × 10 −5 m. In the case of mouse neuroblastoma cells, inorganic mercury stimulated DNA synthesis at 1 to 5 × 10 −6 m and also thymidine transport system at 1 to 2 × 10 −5 m.

The chemotherapeutic exploitation of virus-specified enzymes

The virus-specified thymidine kinase which is induced following infection with herpes simplex virus types 1 and 2 can phosphorylate 9-(2-hydroxyethoxymethyl)guanine (acyclovir, acycloguanosine) and a number of other acyclic analogs of purine nucleosides which are not substrates for the cellular thymidine kinase. Purine deoxyribonucleosides or arabinosides are not good substrates for this virus-coded enzyme; acyclic derivatives of guanine are better substrates than those of pyrimidines or adenine. The potent and selective anti-herpetic activity of acyclovir is due to its conversion to a monophosphate by the viral-specified thymidine kinase, the subsequent conversion to a triphosphate by cellular enzymes, and the inhibition of the herpes virus-coded DNA polymerase by the triphosphate. Acyclovir triphosphate is both an inhibitor and substrate for DNA polymerases. The virus-coded DNA polymerases induced by herpes viruses incorporate acyclovir more rapidly and are more sensitive to inhibition and inactivation than are the cellular α DNA polymerases. The ability of mouse LM cells, thymidine-deficient LM cells (LTK −), and LTK − cells transformed to the LTK + phenotype by HSV-1 or HSV-2 genetic information (LTK −C139, LH 7 and D 21) to anabolize acyclovir has been investigated. The transformed cells converted acyclovir to its mono-, di- and triphosphates, and showed greater sensitivity to growth inhibition by acyclovir than did the untransformed LTK − cells or the original LM line which contains only cellular thymidine kinase. Evidence has been obtained for the inhibition by acyclovir of the elongation of newly synthesized DNA in LH 7 cells, and for the incorporation of acyclovir into the DNA as a chain-terminating event.

Toxicity of naturally occuring purine deoxyribonucleosides

Toxicity of naturally occuring purine deoxyribonucleosides

Bromodeoxyuridine mutagenesis in mammalian cells is stimulated by purine deoxyribonucleosides.

The effects of purine deoxyribonucleosides on bromodeoxyurdine (BrdU) mutagenesis in Syrian hamster melanoma cells were determined. Both deoxyguanosine (dG) and deoxyadenosine (dA) were found to stimulate mutagenesis without changing the amount of BrdU in DNA. In addition, the stimulation of mutagenesis by dG and dA was suppressed by the addition of deoxycytidine (dC). These results suggest that BrdU mutagenesis involves the perturbation of dC metabolism, which perturbation is enhanced by dGTP and dATP. The mutagenic activity of dG in the absence of BrdU was tested, as was that of thymidine (dT), which we had shown previously to stimulate BrdU mutageneis. With dG alone, no increase above the spontaneous mutation frequency was detected. However, at extremely high concentration, dT in the absence of BrdU was slightly mutagenic, and the mutagenesis by dT was enhanced by dG and suppressed by dC.

Deoxyribonucleoside toxicity in adenosine deaminase and purine nucleoside phosphorylase deficiency: implications for the development of new immunosuppressive agents.

The immunodeficient state associated with adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP) deficiency may result from the selective phosphorylation by thymus-derived lymphocytes of the ADA substrate deoxyadenosine and the PNP substrate deoxyguanosine, leading to the intracellular trapping of toxic deoxyribonucleoside triphosphates. Agents such as deoxycytidine might be able to favourably modify the immunodeficient state by inhibiting deoxyribonucleoside phosphorylation. Deficiencies of other nucleotide catabolic enzymes, if selectively expressed by lymphocytes, might also lead to immunodeficiency via nucleoside trapping in lymphoid tissues. Purine deoxyribonucleoside analogues, either alone or in combination with ADA inhibitors, may have value as lymphospecific antimetabolites.

Differential Sensitivity of Human Leukemic T Cell Lines and B Cell Lines to Growth Inhibition by Deoxyadenosine

Abstract Previous experiments have suggested that the lymphospecific toxicity associated with inherited deficiencies of the enzymes adenosine deaminase (ADA) (adenosine aminohydrolase; EC 3.5.4.4) and purine nucleoside phosphorylase (PNP) (purine-nucleoside orthophosphate ribosyltransferase; EC 2.4.2.1) is mediated by toxic purine deoxyribonucleotides, which are selectively trapped in lymphoid tissues enriched in purine deoxyribonucleoside kinase. This hypothesis, however, does not fully explain the greater impairment of T as opposed to B cell functions seen in ADA and particularly PNP deficiency. In the present experiments we have compared the inhibitory effects of deoxyadenosine and adenosine, the natural substrates of ADA, on three leukemic T cell lines and three B cell lines in long-term tissue culture. The leukemic T cell lines were 20-fold more sensitive than the B cell lines to the toxic effects of deoxyadenosine, but not adenosine. In the presence of the ADA inhibitor erythro-9-(2-hydroxy-3-nonyl) adenine hydrochloride, 2.6 µM deoxyadenosine inhibited leukemic T cell growth by 50%. The increased sensitivity of the T cell lines to deoxyadenosine was associated with the accumulation of intracellular deoxyadenosine triphosphate (deoxyATP), and with inhibition of DNA but not RNA synthesis. In both the T and B cell lines, deoxyadenosine toxicity could be reversed by the addition of deoxycytidine to the culture medium. Among other toxic compounds tested, the leukemic T cells were several-fold more sensitive than the B cells to thymidine, a known ribonucleotide reductase inhibitor. Thus leukemic T cells in vitro appear to be very susceptible to the toxic effects of ribonucleotide reductase inhibitors. Purine deoxyribonucleoside analogs that are not substrates for adenosine deaminase or purine nucleoside phosphorylase, and thymidine analogs that are not substrates for thymidine phosphorylase, may have potential value as T cell-selective chemotherapeutic agents.

The reaction of (+/-)-7alpha, 8beta-dihydroxy-9beta, 10beta-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene with DNA.

The reaction of (+/-)-7alpha,8beta-dihydroxy-9beta,10beta-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene (BP diol epoxide) with DNA, followed by enzymatic hydrolysis and LH 20 Sephadex column chromatography, yielded products containing a purine deoxyribonucleoside linked to a 7,8,9,10-tetrahydrobenzo(a)pyrene derivative. DNA containing tritiated adenine or pyrimidines gave little or no tritiated products, showing that reaction occurred chiefly with the guanine residues. Results with 8-(3H)-guanine-labelled DNA, and studies on the protonation and ionization of the products in acid or alkaline media, led to the formulation of the main product as an N2-substituted guanine derivative. The reaction of BP diol epoxide with deoxyadenosine and deoxyguanosine gave further nucleoside derivatives which were probably minor products in the reaction with DNA. Treatment with strong acid unexpectedly converted each of the isolated products to free guanine or adenine.

A DNA polymerase from Ustilago maydis. 2. Properties of the associated deoxyribonuclease activity.

The polymerase and deoxyribonuclease activities of the purified Ustilago maydis DNA polymerase coeluted from a hydroxyapatite column, cosedimented in sucrose gradients in both the absence and presence of salt, possessed similar thermolabilities and reaction requirements. These observations suggest that both activities are associated with the same enzyme and that the deoxyribonuclease activity is not a contaminant. The initial rate of degradation of native 3'-end-group-labelled DNA was similar to that of a heat-denatured substrate, but the final extent was greater for the former. The enzyme exhibits a high specificity for degradation of DNA in a 3' leads to 5' direction. The degradation of a DNA template was inhibited by the presence of the deoxyribonucleoside triphosphates necessary for simultaneous DNA synthesis, but not that of the newly synthesised DNA. About 50%, 29% and 13% of the purine, cytosine and thymine deoxyribonucleotide residues incorporated by the enzyme into DNA respectively, were subsequently excised when monitored by the resulting conversion of the triphosphate substrates to free monophosphate. The majority of the purine deoxyribonucleoside monophosphates appear after the synthetic phase of the reaction has ceased. In many respects, therefore, the deoxyribonuclease activity of the U. maydis DNA polymerase is similar to the bacteriophage T4-induced enzyme.

Intracellular conversions of deoxyribonucleosides by Novikoff rat hepatoma cells and effects of hydroxyurea

AbstractThe incorporation of 3H‐labeled deoxyadenosine and deoxyguanosine into nucleic acids by cultured Novikoff rat hepatoma cells is about 80% into RNA and 20% into DNA. The pathways of incorporation have been elucidated in studies with whole cells and cell‐free extracts. Deoxyadenosine is very rapidly deaminated to deoxyinosine. Most of the deoxyinosine formed by whole cells is transported out of the cells and accumulates in the medium. A portion of the deoxyinosine, and deoxyguanosine are phosphorolyzed by purine nucleoside phosphorylase to hypoxanthine and guanine, respectively. The latter are subsequently converted by hypoxanthine‐guanine phosphoribosyl transferase to IMP and GMP, respectively. Incorporation of the purine deoxyribonucleosides into DNA is mainly via this pathway and the subsequent reduction of ADP and GDP by ribonucleoside reductase, although a small proportion of the deoxyadenosine and deoxyguanosine taken up by the cells seems to be directly phosphorylated to dAMP and dGMP, respectively. Deoxyguanosine is incorporated only into guanine residues of RNA and DNA. Deoxyadenosine is also mainly incorporated into guanine residues of RNA and DNA, although the radioactivity of deoxyadenosine in the acid‐soluble pool is almost exclusively associated with ATP. A similar labeling pattern is observed with labeled deoxyinosine, inosine or hypoxanthine. The pyrimidine deoxyribonucleosides, on the other hand, are specific precursors for their respective bases in DNA.Hydroxyurea inhibits the incorporation of all deoxyribonucleosides into DNA. Results from pulse‐chase experiments indicate that the inhibition of DNA synthesis is prevented by the presence of high concentrations of deoxyadenosine plus deoxyguanosine in the medium. Either purine deoxyribonucleoside alone or deoxycytidine, hypoxanthine or inosine alone or in combination with deoxyadenosine or deoxyguanosine are ineffective. The results are consistent with the conclusion that the inhibition of DNA synthesis is due to a depletion of the dATP and dGTP pools as a result of the hydroxyurea treatment. On the other hand, hydroxyurea causes an increased incorporation of thymidine and deoxycytidine into the dTTP and dCTP pools, respectively. Evidence is presented to indicate that this effect of hydroxyurea is due to an increased synthesis of dTTP and dCTP rather than to an inhibition of their turnover.

Purification and Properties of Purine Nucleoside Phosphorylase from Salmonella typhimurium

Abstract Purine nucleoside phosphorylase (inosine + Pi ⇌ hypoxanthine + α-d-ribose 1-phosphate, EC 2.4.2.1) from Salmonella typhimurium LT-2 has been purified 230-fold. High speed sedimentation equilibrium studies showed that the molecular weight of the native enzyme was 141,000. A molecular weight of 130,000 ± 10% was determined by Sephadex G-150 filtration. Disc gel electrophoresis of the enzyme in the presence of sodium dodecyl sulfate revealed a subunit molecular weight of 23,500, indicating that the enzyme is composed of six subunits. The purified enzyme was found to be specific for the purine ribonucleosides and deoxyribonucleosides, inosine, deoxyinosine, guanosine, deoxyguanosine, adenosine, and deoxyadenosine. The Michaelis constants for inosine, deoxyinosine, and phosphate ion were 50 µm, 47 µm, and 0.37 mm, respectively.

Thymidine 2′-Hydroxylation in Neurospora crassa

An enzyme preparation catalyzing the 2′-hydroxylation of thymidine was prepared from mycelial extracts of Neurospora crassa strain STA 4 (FGSC 262A) by chromatography on hydroxylapatite and DEAE-Sephadex A-50. The enzyme had an isoelectric point of 4.6 and a molecular weight of 47,000 (determined by gel filtration). The reaction product was identical with thymine riboside on ion exchange and thin layer chromatography. Paper chromatography after reduction and hydrolysis showed that the pentose moiety in the product was ribose. Of the pyrimidine deoxyribonucleosides tested as substrates, only those with oxygen at carbon atoms 2 and 4 were active, i.e. deoxyuridine, thymidine, 5-hydroxymethyldeoxyuridine, 5-bromodeoxyuridine, and 6-azathymidine. Thymidylate was attacked only slowly. Purine deoxyribonucleosides, deoxyribose, and 1-ethyluracil were not substrates. No evidence for control by nucleotides was obtained. The enzyme had an absolute requirement for ferrous ion and 2-ketoglutarate, and ascorbate and catalase were stimulatory. 2-Ketoglutarate was oxidatively decarboxylated during the reaction. Together with the previously demonstrated oxygen requirement (S haffer , P. M., M c C roskey , R. P., P almatier , R. D., M idgett , R. J., and A bbott , M.T. (1968) Biochem. Biophys. Res. Commun. 33, 806) the present findings establish that thymidine 2′-hydroxylase belongs to the group of oxygenases which require a 2-keto acid for oxygen reduction (H olme , E., L indstedt , G., L indstedt , S., and T offt , M. (1968) Fed. Eur. Biochem. Soc. Lett. 2, 29; L indblad , B., L indstedt . G., L indstedt , S., and T offt , M. (1969) J. Amer. Chem. Soc. 91, 4604).

The biosynthesis of DNA by insects: IV. Metabolism of purine deoxyribonucleosides during adult development of the Cecropia silkmoth

Injected deoxyadenosine labels both the adenine and guanosine of DNA in developing Cecropia adults, while injected deoxyguanosine is not significantly incorporated. In vitro experiments demonstrate potent deoxyadenosine deaminase activity which converts deoxyadenosine to deoxyinosine. Deoxyinosine serves as precursor for both dAMP and dGMP.

Determination of the nucleoside triphosphate contents of eggs and oocytes of Xenopus laevis.

The ribonucleotide and deoxyribonucleotide contents of eggs and oocytes of Xenopus laevis were measured. Eggs contained most deoxyribonucleotide in the form of triphosphates. dCTP, dTTP, dATP and dGTP were present in similar amounts. The egg contained sufficient deoxynucleotide triphosphate to make approximately 2500 nuclei. Oocytes contained less pyrimidine deoxyribonucleoside triphosphates than did eggs, and purine deoxyribonucleoside triphosphates were not detected. These differences may be correlated with the ability of eggs to induce nuclear DNA synthesis, a property not shown by oocytes. Both oocytes and eggs seem to contain non-phosphorylated, alpha-unsubstituted aldehydes, which may be deoxyribose derivatives. Eggs and oocytes contain similar amounts of ribonucleoside triphosphates. The low rate of RNA synthesis found in eggs, but not in oocytes, is therefore not caused by simple precursor control.