Guanine solubility

As with pyrimidines, the water-soluble carbodiimide CMC may react with guanine derivatives to give a reversible adduct at N-l (Figure 1.52). Raising the pH to highly alkaline conditions regenerates the purine group. Adenine residues, however, display no reactivity in this process. 

When the receptor interacts with its associated G protein, the conformation of the guanine-nucleotide-binding site is altered. The subunits then dissociate, and a phosphatidylinositol-specific phospholipase C (PI-PLC) is activated [5]. The subsequent hydrolysis of phosphatidylinositol bisphosphate then produces inositol triphosphate (IP3) and diacylglycerol (DAG), which are known to be secondary messengers. For example, the water soluble IP3 is released into the cell where its ultimate targets are the calcium storage organelles from which Ca2+ is released [3]. The presence of DAG in cells is known to activate the cellular enzyme protein kinase C (PKC) [6, 7], which phosphorylates a number of cellular... 

For birds, insects, and reptiles, which have an egg stage during development, so that water availability is severely restricted, the synthesis of a highly soluble excretory product would have serious osmotic consequences therefore most of the ammonia is converted to the virtually insoluble uric acid (urate). This product can be safely retained in the egg or excreted as a slurry of fine crystals by the adult. In birds that nest colonially this can accumulate in massive amounts on islands off the coast of Peru cormorants have deposited so much that this guano (hence the name guanine) is collected for use as a fertiliser. Uric acid is less effective as an excretory product, since it has a lower nitrogen content than urea (33%) and is more expensive to synthesise (2.25 molecules ATP per atom of nitrogen). Mammals do produce uric acid but as a product of purine catabolism (see above). 

The effect of 6-mercaptopurine on the incorporation of a number of C-labelled compounds into soluble purine nucleotides and into RNA and DNA has been studied in leukemia L1210, Ehrlich ascites carcinoma, and solid sarcoma 180. At a level of 6-mercaptopurine that markedly inhibited the incorporation of formate and glycine, the utilization of adenine or 2-aminoadenine was not affected. There was no inhibition of the incorporation of 5(or 4)-aminoimidazole-4(5)-carboxamide (AIC) into adenine derivatives and no marked or consistent inhibition of its incorporation into guanine derivatives. The conversion of AIC to purines in ascites cells was not inhibited at levels of 6-mercaptopurine 8-20 times those that produced 50 per cent or greater inhibition of de novo synthesis [292]. Furthermore, AIC reverses the inhibition of growth of S180 cells (AH/5) in culture by 6-mercaptopurine [293]. These results suggest that in all these systems, in vitro and in vivo, the principal site at which 6-mercaptopurine inhibits nucleic acid biosynthesis is prior to the formation of AIC, and that the interconversion of purine ribonucleotides (see below) is not the primary site of action [292]. Presumably, this early step is the conversion of PRPP to 5-phosphoribosylamine inhibited allosterically by 6-mercaptopurine ribonucleotide (feedback inhibition is not observed in cells that cannot convert 6-mercaptopurine to its ribonucleotide [244]. 

This group includes the coenzyme forms of water-soluble vitamin B2 or riboflavin. Synthesis occurs by initial cyclohydrolase action on the guanine ring of GTP and subsequent steps lead to the synthesis of the isoalloxazine ring structure (see structures below). 

Kawamura, K. and Kamoto, F. (2000). Condensation reaction of hexanucleotides containing guanine and cytosine with water soluble carbodiimide. Nucleic Acid Symp. Sen, 44, 217-18. 

Around 1980, Tabushi and coworkers used the lipophilized, DABCO-derived diammonium salt 52 as a phase transfer reagent for the transport of nucleotides in three-phase experiments (H2O-CHCI3-H2O) [75]. Whereas AMP was discriminated in a high degree, for ADP and ATP the acceleration rates were quite similar. The transport rates were significantly diminished for uracil and guanine nucleotides because of the low solubility of the resulting complexes. 

Solubility of the Components of DNA Draw the following structures and rate their relative solubilities in water (most soluble to least soluble) deoxyribose, guanine, phosphate. How are these solubilities consistent with the three-dimensional structure of double-stranded DNA ... 

Senthilkumar K, Grozema FC, Guerra CF, Bickelhaupt FM, Siebbeles LDA (2003) Mapping the sites for selective oxidation of guanines in DNA. J Am Chem Soc 125 13658-13659 Setlow B, Setlow P (1993) Binding of small, acid-soluble spore proteins to DNA plays a significant role in the resistance of Bacillus subtilis spores to hydrogen peroxide. Appl Environ Microbiol... 

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