Nucleoside , nucleotide formation from

Diepoxybutane also reacts with nucleosides, nucleotides and DNA. Adducts at N of adenine were identified in incubations (pH 7) containing deoxyadenosine, deoxyadenosine monophosphate or poly(dA-dT)(dA-dT), as determined by mass spectrometry, or calf tliymus DNA as determined by a high-performance liquid chromatography/ 32P-postlabelling method (Leuratti et al., 1994). By the latter method, the authors demonstrated adduct formation to N of adenine in DNA from Chinese hamster ovary cells incubated with diepoxybutane at 37°C. 

All biosynthetic pathways are under regulatory control by key allosteric enzymes that are influenced by the end products of the pathways. For example, the first step in the pathway for purine biosynthesis is inhibited in a concerted fashion by nucleotides of either adenine or guanine. In addition, the nucleoside monophosphate of each of these bases inhibits its own formation from inosine monophosphate (IMP). On the other hand, adenine nucleotides stimulate the conversion of IMP into GMP, and GTP is needed for AMP formation. 

Free purine bases, derived from the turnover of nucleotides or from the diet, can be attached to PRPP to form purine nucleoside monophosphates, in a reaction analogous to the formation of orotidylate. Two salvage enzymes with different specificities recover purine bases. Adenine phosphorihosyltransferase catalyzes the formation of adenylate... 

DNA polymerases catalyze the formation of polynucleotide chains through the addition of successive nucleotides derived from deoxynucleoside triphosphates. The polymerase reaction takes place only in the presence of an appropriate DNA template. Each incoming nucleoside triphosphate first forms an appropriate base pair with a base in this template. Only then does the DNA polymerase link the incoming base with the predecessor in the chain. Thus, DNA polymerases are template-directed enzymes. 

If free amino acids are to be analyzed in foods or feeds, it is advisable to remove matrix components such as lipids, carbohydrates, and nucleic acids from the sample. Of course, the necessary extraction steps are time-consuming, but higher concentrations of such compounds may severely interfere with the amino acid analysis. After hydrolysis of protein-free mixtures of nucleosides, nucleotides, and nucleic acids, Paddock et al. [38] even observed the formation of amino acids, predominantly glycine. 

In the synthesis of homopolysaccharides the monosaccharide units are activated by the formation of nucleoside diphosphate derivatives from which they are transferred to a nonactivated growing polymer. The following nucleotide coenzymes are used in the synthe of the most common polymers. 

The inhibitory effects of allopurinol and oxipurinol on purine and pyrimidine biosynthesis in human fibroblasts could be explained by formation of their respective ribonucleotides either by HGPRTase (allopurinol) or OPRTase (oxipurinol). The effects of allopurinol-1-ribonucleoside are hardly to be explained. Theoretically the allopurinol-1-ribonucleoside can be converted either to the free base (catalyzed by a purine nucleoside phosphorylase) or to allopurinol-1-ribonucleotide (catalyzed by a nucleoside kinase). According to Utter et al. (4) there seems however to be a lack of kinases in mammals which effectively phosphorylate inosine. Furthermore, indirect experiments of Elion et al. (5), where no detectable nucleotide formation or incorporation into nucleic acids was observed in vivo with Hc-allopurinol would support this. Nevertheless, our results would claim for a direot conversion of allopurin-ol-1-ribonucleoside to allopurinol-1-ribonucleotide in human fibroblast, at least at doses from 10 5 -to 10-3 M. Otherwise we would have to explain the inhibitory effects of allopurinol-1-ribonucleoside by direct influences on purine synthesis, for the other possibility theoretical-... 

Reactions of bases with mercury All bases commonly occurring in nucleic acids react in alkaline media with mercury of the electrode polarized to potentials close to zero and form sparingly soluble compounds [141, 142]. Formation of these compounds with mercury is manifested on voltammetric curves by characteristic anodic peaks or waves. Nucleosides and nucleotides derived from pyrimidines (except pseudouridine) are inactive. The reaction of bases with the mercury electrode was used for elaboration of the cathodic strippig voltammetric... 

Section 28 14 The nucleotide sequence of DNA can be determined by a technique m which a short section of single stranded DNA is allowed to produce its complement m the presence of dideoxy analogs of ATP TTP GTP and CTP DNA formation terminates when a dideoxy analog is incorporated into the growing polynucleotide chain A mixture of polynucleotides dif fermg from one another by an incremental nucleoside is produced and analyzed by electrophoresis From the observed sequence of the comple mentary chain the sequence of the original DNA is deduced... 

Sugar nucleotides are formed from sugar-l-phosphates and nucleoside triphosphates by specific pyrophosphorylase enzymes (Figure 23.18). For example, UDP-glucose pyrophosphorylase catalyzes the formation of UDP-glucose from glucose-l-phosphate and uridine 5 -triphosphate ... 

Most nucleotide sugars are formed in the cytosol, generally from reactions involving the corresponding nucleoside triphosphate. GMP-sialic acids are formed in the nucleus. Formation of uridine diphosphate galactose (UDP-Gal) requires the following two reactions in mammahan tissues ... 

In the preceding sections the conversion of purines and purine nucleosides to purine nucleoside monophosphates has been discussed. The monophosphates of adenosine and guanosine must be converted to their di- and triphosphates for polymerization to RNA, for reduction to 2 -deoxyribonucleoside diphosphates, and for the many other reactions in which they take part. Adenosine triphosphate is produced by oxidative phosphorylation and by transfer of phosphate from 1,3-diphosphoglycerate and phosphopyruvate to adenosine diphosphate. A series of transphosphorylations distributes phosphate from adenosine triphosphate to all of the other nucleotides. Two classes of enzymes, termed nucleoside mono-phosphokinases and nucleoside diphosphokinases, catalyse the formation of the nucleoside di- and triphosphates by the transfer of the terminal phosphoryl group from adenosine triphosphate. Muscle adenylate kinase (myokinase)... 

The effect of phase upon the monomer-dimer equilibrium is pronounced. The quantum yields for dimer formation in liquid-aerated water solution are low (from zero for thymine to 10"2 for other pyrimidines) but the quantum yields for dimer formation in frozen aqueous solutions or in single crystals are much higher (reaching unity in frozen water solution for thymine). The quantum yields for monomerization are uniformly high and are about the same in solution or in solid phase. The net result of this phase effect is that even at optimum wavelengths for dimer formation, the yields of dimers are low in solution and high in solid phases, for all the single bases, nucleosides, or nucleotides. 

S Additional information <2, 4> (<4> formation of a ternary complex, addition of substrates is random [5] <2> ATP-mediated induced-fit of LID in CMPKcoli modulated by CMP leading to a closed conformation of the active site, protected from water [15] <4> the UMP-CMP kinase has a relaxed enantiospecificity for the nucleoside monophosphate acceptor site, but it is restricted to D-nucleotides at the donor site [26]) [5, 15, 26]... 

Glycosyl esters ( sugar nucleotides ) are the glycosyl donors for the formation of wall polysaccharides. Some glycosyl-nucleotides can, in vivo, be synthesized directly from the corresponding monosaccharide, ATP, and the appropriate nucleoside triphosphate. In addition, some... 

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