Mononucleotides, deoxyribonuclease

In the small intestine, ribonuclease and deoxyribonuclease I, which are secreted in the pancreatic juice, hydrolyze nucleic acids mainly to oligonucleotides. The oligonucleotides are further hydrolyzed by phosphodiesterases, also secreted by the pancreas, to yield 5 - and 3 -mononucleotides. Most of the mononucleotides are then hydrolyzed to nucleosides by various group-specific nucleotidases or by a variety of nonspecific phosphatases. The resulting nucleosides may be absorbed intact by the intestinal mucosa, or they may un-... 

A simple approach would be to take small aliquots of the sample and treat them with the enzymes ribo-nuclease (RNase) or deoxyribonuclease (DNase). Digestion of the sample by one of these enzymes would indicate whether the sample is RNA or DNA. Another method is to treat a small sample with alkali, which degrades RNA to mononucleotides, but only denatures DNA to the single-stranded form. 

Deoxyribonuclease I from pancreas breaks down high molecular weight deoxyribonucleic acids into oligonucleotides and a small amount of mononucleotides large parts of the polynucleotide structure are unaffected. Ribonucleic acids are unattacked. Deoxyribonucleases from snake venom are capable of breaking down deoxyribonucleic acids more completely than is the deoxyribonuclease I from pancreas. These enzymes have, however, not yet been adequately investigated. 

Reaction of Deoxyribonuclease. DNAase -acts on polymers of various lengths and forms a mixture of oligonucleotides with very little mononucleotide. Dinucleotides containing purines, pyrimidines, and both have been isolated from digests. The substrate specificity is obviously not so restricted as that of pancreatic RNAase, but has yet to be defined completely. The mechanism of action is also obscure. The linkage of phosphate to the 3 position is split by pancreatic DNAase the monoesters found in the products are all 5 -phosphates. From analogy with ribonucleic acid metabolism, it may be anticipated that DNAase with different specificities will be found, and that some will be found to split the 5 ester bonds. 

Deoxyribonucleic Acid, Since only carbons 3 and 5 of the 2-deoxyribose are available for esterification in DNA, the linkages are all most probably of the 3, 5 -type. Purified phosphodiesterase quantitatively liberates 5 -mononucleotides from thymus DNA 100), On the other hand, no method has as yet been developed for degradation of these nucleic acid to 3 -deoxy-mononucleotides, although the pyrimidine 3, 5 -diphosphates have been isolated from acid hydrolyzates of DNA. Crystalline pancreatic deoxyribonuclease rapidly degrades DNA to very low molecular weight polynucleotides, but identification of many of these products reveals no certain route for the action of the enzyme 168),... 

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