DNases spleen phosphodiesterase

As mentioned briefly above, the enzymatic excision of damaged nucleobases may cause some problems. A case in point is the action of nuclease PI. While a single 8-oxo-G lesion is excised as the damaged nucleoside, the clustered 8-oxo-G/Fo lesion is only obtained as modified dinucleotide (Maccubbin et al. 1992). Another example is the hydrolysis of dG pC which severely inhibits the action of bovine spleen phosphodiesterase, while HMUrapA shows only very little inhibition (Maccubbin et al. 1991). Enzymatic hydrolysis of DNA is, in fact, the recommended method for the determination of HMUra (Teebor et al. 1984 Frenkel et al. 1985). It is recalled that mammalian cells cope with this DNA lesion with the help of a hydroxymethyluracil glycosylase (Hollstein et al. 1984). 

Two diastereoisomers have been identified as radiation induced decomposition products of dC. The synthesis of one of these isomers, (5 5,55,6S)-5, 6-cyclo-5-hydroxy-5,6-dihydro-2 -deoxyuridine (81), and its incorporation into DNA, has been reported The presence of the lesion causes a marked destabilisation of DNA duplexes. The nucleases PI, calf spleen phosphodiesterase and bovine intestinal mucosa phosphodiesterase failed to cleave the lesion, nor was it a substrate for a number of repair enzymes, and it acted as a block to Klenow fragment and Taq polymerases. 

Bovine spleen phosphodiesterase hydrolyzes both polyribo- and polydeoxyribonucleotides Figure 5-43 Some hydrolytic cleavage reactions of polynucleotides. Reactions of both RNA and DNA are included. 

Figure 11.18 shows the mass spectrum of the 5 -exonuclease degradation of a DNA 12-mer 5 -d(GCTTXCTCGAGT)-3 digested with calf spleen phosphodiesterase (CSP). Five peaks are observed, which (if the sequence was unknown)... 

Stable hybrids with DNA and may enter cells through passive transport mechanisms. Finally, and potentially important for drug delivery, we have shown that the boranophosphates are nuclease resistant (12), like the phosphorothioates and methyIphosphonates. Short boranophosphate oligomers exhibit a high degree of stability to spleen phosphodiesterase and snake venom phosphodiesterase, indicating that they could have long half-lives in the cell. 

Fig. 2. Proposed structural requirements for substrates of phosphodiesterases that hydrolyze DNA and RNA, those from (a) snake venom, (b) spleen, and (c) staphylococcus (R = thymine and R — p-nitrophenyl). The studies indicated for the venom and spleen enzymes are those suggested by Khorana (67) [data from Cuatrecasas el al. (61)).

Phosphodiesterase II Bovine spleen RNA and DNA (single-stranded) exonudease splits d linkages at 5 end, releasing 3 -phosphonudeosides... 

Spleen (and micrococcal) phosphodiesterase. These exonucleases act on DNA and RNA in a direction that is the reverse of snake venom phosphodiesterase, i.e., they start from the 5 -OH and yield sequentially 3 -phosphates. They... 

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