Nucleotide pools

PDE1C2 and PDE4A are expressed. PDE1C2 is found in the cilia of the epithelium, where it colocalizes with adenylyl cyclase. PDE4A is found throughout the epithelial layer, but not in cilia. Therefore, as in the kidney mesangial cells, different PDEs must be working on different cyclic nucleotide pools. More recently, substantial data has been developed for compartmenta-tion of cAMP and PDEs in cardiac myocytes. 

Fig. 5.1 Regulators of pre- and post-integration latency. Pre-integration latency is regulated as the viral RNA is reverse transcribed into the proviral DNA (A). This is controlled by the avaUabdity of the nucleotide pool, half life of the forming proviral cDNA copy, and the interaction of the viral protein Vif with the cellular antiviral protein APOBEC, espedaUy family members 3G and 3R It is also regulated at the step of transport across the nuclear membrane through the availability of ATP as the process requires energy (B). Post-integration, the proviral DNA copy of the viral genome, is regulated maiiily by the avadabdity of host transcription factors, especially NF-kB and NFAT (C)...

Nucleotide pools and transmembrane potential in bacteria after exposure to penta-chlorophenol were investigated using P NMR. Differences were used to differentiate Escherichia coli, which does not degrade this substrate and a Flavobacterium sp., which is able to do so (Steiert et al. 1988). 

Mo, J.Y., Maki, H. and Sekiguchi, M. (1992). Hydrolytic elimination of a mutagenic nucleotide, 8-oxodGTP, by human 18-kilodalton protein sanitization of nucleotide pool. Proc. Natl Acad. Sci. USA 89, 11021-11025. 

Much research has centered on identifying the source of the purine ring in caffeine. Two possible sources are likely methylated nucleotides in the nucleotide pool and methylated nucleotides in nucleic acids. Extensive experimental work by Suzuki and Takahashi27-30 proposes a scheme whereby caffeine is synthesized from methylated purines in the nucleotide pool via 7-methylxanthosine and theobromine. Information relating to the formation of 7-methylxanthine from nucleotides in the nucleotide pool is sparse. They also provide data that demonstrate that theophylline is synthesized from 1-methyladenylic acid through 1-methylxanthine as postulated by Ogutuga and Northcote.31... 

Low levels or absence of adenosine deaminase (ADA) is associated with one form of severe combined immunodeficiency disease (SCID) characterized by B-andT-lymphocyte dysfunction due to toxic effects of deoxyadenosine (HI9). Most patients present as infants with failure to thrive, repeated infections, severe lymphopenia, and defective cellular and humoral immunity. Disease severity is correlated with the degree of deoxyadenosine nucleotide pool expansion and inactivation of S-adenosylhomocysteine hydrolase in red blood cells. Up to now, more than 40 mutations have been identified (A4, H20, S5, S6). The majority of the basic molecular defects underlying ADA deficiency of all clinical phenotypes are missense mutations. Nonsense mutations, deletions ranging from very large to single nucleotides, and splicing mutations have also been reported. It is likely that severe... 

M. Anglana, F. Apiou, A. Bensimon, and M. Debatisse, Dynamics of DNA replication in mammalian somatic cells Nucleotide pool modulates origin choice and interorigin spacing. Cell 114, 385-394 (2003). 

Fluoropyrimidines cause changes in nucleotide pools that alone increase the cytotoxicity of radiation (i.e., by depleting substrates used in the repair of radiation-induced DNA damage). 

One hypothesis for fluoropyrimidine-induced radiosensitization is that fluoropyrimidines induce changes in nucleotide pools including the ability of polymerases to... 

Ribavirin is a synthetic guanosine analogue that possesses broad antiviral inhibitory activity against many viruses, including influenza A and B, parainfluenza, RS V, HCV, HIV-1, and various herpesviruses, arenaviruses, and paramyxoviruses. Its exact mechanism of action has not been fully elucidated however, it appears to inhibit the synthesis of viral mRNA through an effect on nucleotide pools. Following absorption, host cell enzymes convert ribavirin to its monophosphate, diphosphate, and triphosphate forms. Ribavirin monophosphate... 

In the transfer of reducing equivalents from the pyridine nucleotide pool, flavoproteins carry out a central role of mediating the conversion of the obligatory 2-electron reductant to 1-electron receptors such as hemes and iron-sulfur redox centers. In such a role, the semiquinone form of the flavin serves as a pivotal intermediate. The reduction of flavins and flavoproteins by reduced pyridine nucleotides has been extensively studied since the initial work of Singer and Kearney which showed that flavin reduction can occur in a non-enzyme catalyzed manner. The reduction proceeds as a 2-electron process since the formation of a nicotinamide semiquinone (a necessary intermediate in a 1-electron process) has been... 

A quantitative description of oxidative phosphorylation within the cellular environment can be obtained on the basis of nonequilibrium thermodynamics. For this we consider the simple and purely phenomenological scheme depicted in Fig. 1. The input potential X0 applied to the converter is the redox potential of the respiratory substrates produced in intermediary metabolism. The input flow J0 conjugate to the input force X0 is the net rate of oxygen consumption. The input potential is converted into the output potential Xp which is the phosphate potential Xp = -[AG hoS -I- RT ln(ATP/ADP P,)]. The output flow Jp conjugate to the output force Xp is the net rate of ATP synthesis. The ATP produced by the converter is used to drive the ATP-utilizing reactions in the cell which are summarized by the load conductance L,. Since the net flows of ATP are large in comparison to the total adenine nucleotide pool to be turned over in the cell, the flow Jp is essentially conservative. 

Although much remains to be discovered about the details of the regulation of nucleotide metabolism, a number of important control points are rather well understood. We discuss some of these here, together with their known effects on intracellular nucleotide pools. 

There are also changes in the rates of metabolism as red blood cells appear and aerobic processes intensify (Lasker and Theilacker, 1962 Laurence, 1975 Timeyko and Novikov, 1991) during the early phases of ontogenesis. Oxygen consumption increases, as do the number of mitochondria and their protein contents (Abramova and Vasilyeva, 1973 Ozemyuk, 1993). The adenyl nucleotide pool (ATP and ADP) decreases (Milman and Yurovitsky, 1973 Boulekbache, 1981), while the activity of cytochrome oxidase increases (Ozemyuk, 1993). The increased energy metabolism corresponds to a considerable extent with motor activity (Reznichenko, 1980). In the yolk sac, the activity of proteinase, which supplies nitrogenous materials to the embryo, increases, as does the rate of amino acid incorporation into the body proteins. 

The increase with time in the incorporation of radioactivity into DNA is linear between 30 and 90 min of the concomitant addition of drug and tritiated thymidine and during this time the specific activity of the acid soluble nucleotide pool remains constant and identical to that of the supplied [3H]thymidine. 

In leukemia cells treated with methotrexate, levels of dTTP decrease, and there may be less marked decreases in dATP and dGTP resulting from inhibition of amido PRTase. The consequent imbalance in nucleotide pools results in genetic miscoding and cell death. 

The total NADase activity of tissues from these four enzymes is very high, and the total tissue content of nicotinamide nucleotides can be hydrolyzed within a few minutes. Two factors prevent this in vivo. Apart from NAD pyrophosphatase, the enzymes that catalyze the release of nicotinamide from NAD(P) are biosynthetic rather than catabolic, and their activity is highly regulated under normal conditions. Furthermore, the values of K n of the enzymes are of the same order of magnitude as those of many of the NAD(P)-dependent enzymes in the cell, so that there is considerable competition for the nucleotides. Only that relatively small proportion of the nicotinamide nucleotide pool in the cell that is free at any one time will be immediately available for hydrolysis. 

Figure 7 shows the response of the redox potential in a perfused hamster liver to the addition of 45 mN ethanol. Instead of the vitro labeling strategy Just described. the pyridine nucleotide pools in this hamster liver were labeled vivo by intraperitoneal injection of 35 mg [5- C] nicotinamide 5 hours prior to sacrifice. The bottom two spectra (2.6 min and 12.8 min) were obtained prior to addition of ethanol. They show resonances from labeled NAD, natural abundance glycogen and natural abundance choline methyl groups of phospholipids but no resonance from reduced pyridine nucleotides. After addition of 45 mM 10% [1- C] ethanol (at 17.9 min), resonances from C-1 of ethanol and NADH are detectable. These data demonstrate that the pyridine nucleotide pools labeled by intraperitoneal injection are metabolically active and that addition of 45 mN ethanol results in a marked change in the redox potential of the liver as measured by NNR. Furthermore, the observation of separate resonances for the oxidized and reduced pyridine nucleotides indicates that chemical exchange between oxidized and reduced forms is slow on the NNR time scale, and demonstrate that NNR may be used to quantitate the redox potential of free pyridine nucleotides situ. 

Karl, D. M., and Bossard, P. (1985). Measurement and significance of ATP and adenine-nucleotide pool turnover in microbial-ceUs and environmental samples. J. Microbiol. Methods 3, 125—139. 

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