Nucleic acids degradation

Other systems like electroporation have no lipids that might help in membrane sealing or fusion for direct transfer of the nucleic acid across membranes they have to generate transient pores, a process where efficiency is usually directly correlated with membrane destruction and cytotoxicity. Alternatively, like for the majority of polymer-based polyplexes, cellular uptake proceeds by clathrin- or caveolin-dependent and related endocytic pathways [152-156]. The polyplexes end up inside endosomes, and the membrane disruption happens in intracellular vesicles. It is noteworthy that several observed uptake processes may not be functional in delivery of bioactive material. Subsequent intracellular obstacles may render a specific pathway into a dead end [151, 154, 156]. With time, endosomal vesicles become slightly acidic (pH 5-6) and finally fuse with and mature into lysosomes. Therefore, polyplexes have to escape into the cytosol to avoid the nucleic acid-degrading lysosomal environment, and to deliver the therapeutic nucleic acid to the active site. Either the carrier polymer or a conjugated endosomolytic domain has to mediate this process [157], which involves local lipid membrane perturbation. Such a lipid membrane interaction could be a toxic event if occurring at the cell surface or mitochondrial membrane. Thus, polymers that show an endosome-specific membrane activity are favorable. 

Nucleic acid degradation in humans and many other animals leads to production of uric acid, which is then excreted. The process initially involves purine nucleotides, adenosine and guanosine, which are combinations of adenine or guanine with ribose (see Section 14.1). The purine bases are subsequently modified as shown. 

A. Salvage pathways allow synthesis of nucleotides from free purines or pyrimidines that arise from nucleic acid degradation or dietary sources, which is more economical for the cell than de novo synthesis. 

Dietary purines are not an important source of uric acid. Quantitatively important amounts of purine are formed from amino acids, formate, and carbon dioxide in the body. Those purine ribonucleotides not incorporated into nucleic acids and derived from nucleic acid degradation are converted to xanthine or hypoxanthine and oxidized to uric acid (Figure 36-7). Allopurinol inhibits this last step, resulting in a fall in the plasma urate level and a decrease in the size of the urate pool. The more soluble xanthine and hypoxanthine are increased. 

Lewis, A.D. et al. (1992) Role of cytochrome P-450 from the human CYP3A gene family in the potentiation of morpholino doxorubicin by human liver microsomes, Cancer Res. 52, 4379-4384. Feinstein, E. et al. (1993) Dependence of nucleic acid degradation on in situ free-radical production by Adriamycin, Biochemistry 32, 13156-61. 

A close look at this reaction reveals that in the opposite direction, the reaction is of the phosphorolysis type. For this reason, the enzymes catalyzing the reaction with ribose-l-phosphate are called phosphorylases, and they also participate in nucleic acid degradation pathways. Purine nucleoside phosphorylases thus convert hypoxanthine and guanine to either inosine and guanosine if ribose-l-phosphate is the substrate or to deoxyinosine and deoxyguanosine if deoxyribose-1-phosphate is the substrate. Uridine phosphorylase converts uracil to uridine in the presence of ribose-l-phosphate, and thymidine is formed from thymine and deoxyribose-l-phosphate through the action of thymidine phosphorylase. 

Failure to amplify the internal control may be due to nucleic acid degradation, inhibitors of amplification, or amplification failure. Regardless of the cause, when the internal control is not detected the assay is invalid. 

Cancer patients may experience gout as a result of chemotherapy, which generates many purines by nucleic acid degradation after cell death. 

Nucleic Acid Degradation and the Importance of Nucleotide Salvage (Figure 22.2, Diagram)... 

Inside the endosome the pH (5.0-6.2) is more acidic and poses the problem of nucleic acid degradation. In the case of viral vectors, their inherent property to undergo conformational changes in the coat proteins promotes endosomal membrane fusion, which helps in protecting them from the endosomal environment, but in the case of nonviral vectors, lysosomotropic agents like chloroquine, membrane-destabilizing peptides such as synthetic N-terminal peptides of rhinovirus VP-1 or influenza virus HA-2 are attached to the cationic complex to mediate endosomal release. 

Fixed tissue is generally processed for cryostat sectioning, but in situ hybridization can be equally successful on paraffin embedded tissue (8,9). In any case, it is important always to keep the delay between tissue collection and fixation to a minimum, to avoid nucleic acid degradation, which obviously increases with time delay (4,10). This... 

Xanthine, or 2,6-dihydroxypurine, was first associated with caffeine in certain plants. It was later found in urine, blood, and liver. In 1817, Marcet detected xanthine in renal calculi. Xanthine was synthesized from chloropurine or from 4-aminouracil. An addition to its biological significance as the product of nucleic acid degradation (deamination of guanine or oxidation of hypoxanthine), xanthine is also important as an... 

The uric acid formed from nucleic acid degradation of endogenous or exogenous nucleic acids is excreted as such without chemical alteration in higher apes and man. (In the dalmatian uric acid is partly oxidized and partly excreted.) In all other mammals, uric acid is further oxidized to yield allantoin, and uricase is the enzyme that catalyzes that reaction. In amphibians, fish, and many invertebrates, two more enzymes exist one involved in the oxidation of allantoin to allantoic acid (allantoinase), the other catalyzing the splitting of allantoic acid to yield urea and glyoxylic acid. 

DNA-modifying enzymes, which synthesize nucleic acids, degrade them, join pieces... 

Extracellular free amino acids are usually those commonly found in protein. Some non-protein amino acids, such as y-aminobutyric acid and )8-amino acids, also occur. Low levels of )8-amino acids are usually products of nucleic acid degradation. 

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