Guanine and adenosine

A second sample of DNA is treated with a piperidine-formate buffer of pH 2 in the cold. This promotes the acid depurination of both guanine and adenosine. 

The existence of two separate enzymes in animal tissues responsible for the liberation of ammonia from each of the two aminopurines, adenine and guanine, the latter specific for the free purine and the former for the nucleosides, was initially presented by Jones and his colleagues 11, 12). In 1928, Schmidt 13-15) demonstrated that AMP aminohy-drolase was responsible for the appearance of inosinic acid in muscle and for at least a portion of ammonia liberated during contraction. He showed not only a marked specificity for deamination of 5 -AMP but also provided the first clue that muscle adenylic acid (5 -AMP) and yeast adenylic acid (3 -AMP) were different compounds. Initial evidence for guanine and adenosine aminohydrolase including aspects of the specificity were also described by Schmidt 16). Additional details regarding development of interest in purine aminohydrolases are available in several excellent reviews 17-20). 

The role of DNA in storing and transferring genetic material is dependent on the properties of the four bases. These bases are complementary in that guanine is always associated with cytosine, and adenosine with thymine. Watson and Crick, some 40 years ago, showed that the stability of DNA is due to the double helix structure of the molecule that protects it from major perturbations. Information is ultimately transferred by separating these strands which then act as templates for the synthesis of new nucleic acid molecules. 

Although the hybridization of single-stranded DNA to its complement results in detectable changes in electrochemical properties, particularly in support of non-Faradaic current, the DNA bases may also demonstrate redox behavior that gives rise to Faradaic currents. The electrochemical behavior of DNA has been studied over the past few decades. Differential pulse voltammograms show clearly defined peaks for the reduction of cytosine and adenosine. Electrochemical characterization of guanine by cyclic voltammetry has shown... 

A guanosine aminohydrolase preparation from Pseudomonas convexa No. 149 free from guanine, adenine and adenosine aminohydrolase and nucleoside phosphorylase activities has been described (63). Of the 22... 

The adsorptive and voltammetric characteristics of Cu(II) complexes with guanine, guanosine and adenosine were exploited [120] in order to detect these bases after separation by capillary zone electrophoresis, and the enzyme-mimic catalytic activity of a DNA-Cu2+ complex [121] was used to develop an amperometric quinacrine sensor using an oxygen electrode covered by the complex entrapped in polyacrylamide gel. 

The purines are exceptional when compared to the majority of heterocyclic compounds in that the most useful starting materials for their preparation are often of natural occurrence. This reflects of course the widespread occurrence of adenine and guanine and their nucleosides as components of nucleic acids. Thus adenine and guanine may be obtained by acid hydrolysis of nucleic acid (38CB718) and hypoxanthine is readily produced by deamination of adenine with nitrous acid (38CB718) or by adenosine deaminase. 

Figure 2 The components of RNA. (a) The primary bases of RNA, which includes the purines adenine and guanine and the pyrimidines cytosine and uracil, (b) A purine nucleoside (adenosine) and a pyrimidine nucleoside (uridine), (c) The nucleotide adenosine 5 -triphosphate. (d) An RNA strand with the sequence AGCU.

The exchange reaction of amino functions with alkyl-, arylalkyl- and arylamino groups, which is particularly useful in the synthesis of pyrimidines, works also in some cases with purines. Adenine was converted into A -benzyladenine (15).Guanine does not react with amine hydrochlorides and adenosine is degraded to adenine. 

In maintaining the structure of DNA, interactions occur between dA and dT, and betw een dG and dC, Adenosine and thymine are complementary bases, while guanine and cytosine arc complementary bases. 

Maxam-Gilbert DNA sequencing relies on mcthylation of guanosine and adenosine nitrogens. Use SpartanView to examine electrostatic potential maps of 9-methyl-guanine and 9-methyladenine, and compare the electrostatic potentials at positions 7 on guanine and 3 on adenine. Which molecule is the better nucleophile, and why ... 

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