Ribosenucleic acid, desoxy

In the early attempts to identify the nitrogenous bases of desoxy-ribosenucleic acid, some confusion arose for two reasons. At first, the products obtained by hydrolysis of nucleoprotein were studied, and there was no assurance that any particular base came from the nucleic acid rather than from the protein. Then, when the nucleic acid itself became available, the hydrolytic agents at first employed were sufficiently drastic to cause some deamination of the amino-purines (with the production of some xanthine and hypoxanthine) and some demethylation of thymine to uracil. In 1874, Piccard isolated guanine (and h3T>oxanthine) from sperm nuclein. Kossel and Neumann discovered in the hydrolysate of thymus nucleic acid two new pyrimidine bases which they named thy-mine and cytosine but they assigned incorrect empirical formulas to them. In 1894, they correctly described thymine as CsHgOjNs, but cytosine was not purified and characterized till much later. " " Levene now analyzed a series of nucleic acids from a variety of sources and found " that they all contained guanine and adenine. By mild hydrolysis of thymus nucleic acid, Steudel obtained guanine and adenine as the sole purine bases and demonstrated that they occur in equi-molecular proportions. Levene and Mandel confirmed this result and showed that the two purine bases and the two pyrimidine bases (thymine and cytosine) all occur in thymus nucleic acid in equimolecular proportions. 

The diphosphosugar should be studied further, since it offers the chance of identifying the sugar of the pyrimidine nucleosides of desoxy-ribosenucleic acid. There is every reason to believe that the sugar is 2-desoxy-D-ribose, but no definite proof is yet forthcoming. 

Cohen s studies of electrophoretic mobility of samples of desoxy-ribosenucleic acid isolated in different ways, indicate that the acid may possess either four or five acidic groups per tetranucleotide unit, depending upon the previous treatment. Indeed, according to Bredereck, depolymerization to the pentabasic tetranucleotide state can be induced by treatment of the polymer with dilute sodium hydroxide at 60 , followed by neutralization with acetic acid and two precipitations with alcoholic hydrochloric acid at 10 . This supposed tetranucleotide did not form a gel or exhibit streaming birefringence it had a molecular weight of 1,196 to 1,274. 

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