DATP 2 -deoxyadenosine 5 -triphosphate

Dansyl-CaM, dansyl-calmodulin Dansyl-CaM-FC, Ca2 1 -dependent dansyl-calmodulin fluorescence change dATP, 2 -deoxyadenosine 5 -triphosphate DB, diabetic... 

Regulation of ribonucleotide reductase is complex. The binding of dATP (deoxyadenosine triphosphate) to a regulatory site on the enzyme decreases catalytic activity. The binding of deoxyribonucleoside triphosphates to several other enzyme sites alters substrate specificity so that there are differential increases in the concentrations of each of the deoxyribonucleotides. This latter process balances the production of the 2 -deoxyribonucleotides required for cellular processes, especially that of DNA synthesis. 

Pentostatin (deoxycoformycin Fig. 4) is a purine isolated from cultures of Streptomyces antibioticus. Its mode of action involves inhibition of adenosine deaminase, which plays a key role in purine salvage pathways and DNA synthesis. As a consequence, deoxyadenosine triphosphate (dATP) is accumulated, which is highly toxic to lymphocytes. This is associated with augmented susceptibility to apoptosis, particularly in T cells. 

Adenine Deoxyadenosine Deoxyadenyiic acid Deoxyadenosine monophosphate (dAMP) Deoxyadenosine diphosphate (dADP) Deoxyadenosine triphosphate (dATP)... 

Tenofovir disoproxil fumarate (Viread) is a prodrug of tenofovir, a phosphorylated adenosine nucleoside analogue, and is the only available agent of its class. It is converted by cellular enzymes to tenofovir diphosphate, which competes with deoxyadenosine triphosphate (dATP) for access to reverse transcriptase and causes chain termination following its incorporation. Tenofovir was approved as part of a combination therapy for HIV in adults who failed treatment with other regimens it appears to be effective against HIV strains that are resistant to NRTIs. The pharmacokinetic properties of tenofovir are provided in Table 51.2. 

When two acid molecules condense by elimination of a molecule of water, the product is called an acid anhydride, as can be seen in Figure 12.60. Acid anhydrides are always very reactive, or high-energy, compounds. When deoxy-adenosine monophosphate forms an anhydride with phosphoric acid, we have deoxyadenosine diphosphate (dADP). Of course, if we add an additional phosphate group, we have deoxyadenosine triphosphate (dATP). 

A Abe ACE ACh ADME ADR Ala Arg Asp ATP dATP AUC Adenine Abequose Angiotensin-converting enzyme Acetyl choline Absorption, distribution, metabolism and elimination Adverse drug reaction Alanine Arginine Aspartate Deoxyadenosine triphosphate Adenosine triphosphate Area under the curve... 

For example, the rate of reaction of ribonucleotide reductase is regulated by deoxyadenosine triphosphate (dATP) which is a product of the pathway for which ribonucleotide reductase is the committing step (Fig. 8.9). Note that dATP is neither a substrate nor a product of ribonucleotide reductase itself rather, it is an allosteric inhibitor. If the pathway (NDP dNTP) is running at a rate too high for the rate at which dNTPs are being used (for DNA synthesis), the concentrations of the dNTPs will rise, including [dATP], The increase will "feed back" to ribonucleotide reductase by the... 

Pemetrexed and its polyglutamates have a somewhat different spectrum of biochemical actions. Like methotrexate, it inhibits DHFR, but as a poly glutamate, even more potently inhibits glycinamide ribonucleotide formyltransferase (GART) and TS. Unlike methotrexate, it produces little change in the pool of reduced folates, indicating that the distal sites of inhibition (TS and GART) predominate. Its pattern of deoxynucleotide depletion also differs, with little effect on deoxyadenosine triphosphate (dATP), a profile more characteristic of primary TS inhibition. 

There are three plausible mechanisma to explain malaria parasite killing following vivo deoxycoformycin inhibition of ADA. First, there could be an IE deficiency of the catabolite hypoxanthine which is needed by the parasite for nucleotide synthesis. Second, there may be direct toxicity to critical parasite enzymes from accumulated adenosine or deoxyadenosine. Increased levels of 2 -deoxyadenosine, for example, have been shown to irreversibly inactivate S-adenosylhomocysteine hydrolase due to accumulation of S-adenosylhomocysteine which inhibits methyltrans-ferase reactions (9). Third, there could be an accumulation of deoxyadenosine triphosphate, dATP, such as has been observed in ADA associated severe combined immunodeficiency disease (SCID) CIO). DeoxyATP could act to inhibit ribonucleotide reductase and thereby interfere with DNA synthesis (11). In line with this third mechanism we observed an accumulation of both dADP and dATP in nucleotide profiles (24 hr) of PEBC following in vivo 2 -deoxycof ormycin treatment of the IP. knowlesi infected rhesus monkeys. 

The consequence of ADA deficiency is accumulation of adenosine and 2 -deoxyadenosine, substances toxic to lymphocytes, important cells in the immune response. 2 -Deoxyadenosine is particularly toxic because its presence leads to accumulation of its nucleotide form, dATP, an essential substrate in DNA synthesis. Elevated levels of dATP actually block DNA replication and cell division by inhibiting synthesis of the other deoxynncleoside 5 -triphosphates (see Chapter 27). Accumulation of dATP also leads to selective depletion of cellular ATP, robbing cells of energy. Children with ADA SCID fail to develop normal immune responses and are susceptible to fatal infections, unless kept in protective isolation. 

The biologic action of gemcitabine on its own is due almost completely to its effects on DNA metabolism. Early studies of this drug in leukemic cell lines showed that notable decreases in cellular dNTPs occurred with the use of the drug (8). These decreases were most impressive in terms of the levels of 2 -deoxycytidine 5 -triphosphate (dCTP), however, 2 -deoxyadenosine 5 -triphosphate (dATP) and 2 -deoxyguanosine 5 -triphosphate (dGTP) were also affected. It is felt that part of this is due to the inhibitory effects of... 

Deoxyadenosine 5 -Triphosphate (dATP) 100 mM solution, pH 7.5 (Pharmacia Biotech, Piscataway, NJ)... 

Radiochemicals tritiated 2 -deoxythymidine 5 -triphosphate [me/fty/-3H]dTTP, 2 -deoxyadenosine 5 -triphosphate [2,8-3H]dATP, 2 -deoxyguanosine 5 -triphos-phate [8-3H]dGTP or 2 -deoxycytidine 5 -triphosphate [5-3H]dCTP. The radiospecificities of the deoxy nucleotides usually range between 15 and 30 Ci/mmol. They can be obtained from several companies such as Amersham (Buckinghamshire, UK), ICN (Costa Mesa, CA), NEN (DuPont Ltd., Hertfordshire, UK), Moravek Biochemicals (Brea, CA), and so forth. They can be used at 2 pCi/assay. 

The synthesis of the two diastereoisomers of P -l-(2-nitrophenyl)ethyl adenosine S -lri-phosphate (91) has been achieved using resolved (R)- and (5)-l-(2-nilroidienyl)ethanol. The alcohols were converted to (R)- and (5)-l-(2-nitrophenyl)ethyl phosphates by phosphitylation with N,)V-diisopropyl-fi(s-(2-cyanoethyl)phosphoramidite (92) and subsequent oxidation with 3-chlorobenzoic acid. Each of the monophosphates was activated with carbonyidiimidazole and condensed with adenosine diphosphate to give the desired triphosphate. These ATP analogues can be used for the rapid release (by flash photolysis) of ATP in biological systems. The 8-azido-3 -0-anthraniloyl derivatives of 2 -dADP (93) and 2 -dATP (94) have been prepared in seven steps from 8-azido-2 -deoxyadenosine. These compounds are of interest as fluorescent and photoactivatable probes for the nucleotide binding site of kinases and cyclases. In particular, (94) was shown to be a competitive inhibitor of Bordetella pertussis adenylate cyclase and the observed K- (74 pM) was close to tiiat predicted from the K- value of 3 -0-anthraniloyl-2 -dATP. ... 

Because dATP would directly activate the luciferase reaction, deoxyadenosine a-thio triphosphate (dATPaS) is used as a substitute for dATP. It is efficiently used by the DNA polymerase, but is not recognized by luciferase. 

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