Endonuclease inhibition

Wu, R. S., Hurst-Calderone, S., and Kohn, K. W. (1987) Measurement of () -alkylguanine-DNA-alkyltransferase activity in human cells and tumour tissues by restriction endonuclease inhibition. Cancer Res. 47, 6229-6235. 

Nebularine. Nebularine(44) is a naturaHy occurring purine riboside isolated from S.jokosukanensis (1,3,4). It is phosphorylated, and inhibits purine biosynthesis and RNA synthesis, but is not incorporated into RNA by E. coli RNA polymerase. It has also found appHcation as a transition state analogue for treatment of schistosomiasis and as a substrate for the restriction endonuclease, Hindll (138—141). 

Endonuclease-catalyzed hydrolysis of DNA at the internucleosomal linker regions into multimers of 180 base pairs which are visualized by electrophoresis as a ladder of nuclear DNA fragments. Access of the endonuclease to DNA is facilitated by depletion of polyamines, and the activity of the enzyme is mcrea.sed by and decreased by ADP-tibosylation. Thus, agents that increase intracellular Ca " or inhibit l>oly(ADP-ribose) polymerase can induce apoptosi.s. ... 

Second, the efficiency of exonucleases and endonucleases in hydrolysing DNA is greatly affected by modification of the bases (Dizdaroglu et /., 1978 Breimer, 1991). For example, Maccubbin et al. (1991) reported that the presence of 8-OH-Gua severely inhibits digestion of dinucleotides by phosphodiesterase. Thus it is not always certain that modified bases are completely hydrolysed from DNA, especially when published hydrolysis techniques are transplanted from one laboratory to another and not revalidated. 

The most recent advances on enzymatic inhibition are related to endonucleases and polymerases. A tris-malonic acid fullerene derivative can interfere with DNA restrictive enzymatic reactions, demonstrating a dose-dependent inhibition of these enzymes, with an IC50 in the micromolar range. The addition of ROS scavenger does not revert the enzymatic activity, indicating that the fullerene action should be exerted in a direct way (Yang et al., 2007d). 

Yang X, Chen Z, Meng X, Li B, Tan X (2007d) Inhibition of DNA restrictive endonucleases and Taq DNA polymerase by trimalonic acid Cm. Chin. Sci. Bull. 52 1802-1806. 

Kuzuhara T, Iwai Y, Takahashi H, Hatakeyama D, Echigo N. (2009) Green tea catechins inhibit the endonuclease activity of influenza A virus RNA polymerase. PLoS Curr Influenza RRN1052. 

In aminoglycoside-treated animals, the cells can be led to canonical apop-totic death through activation of caspases. Caspase-9 forms an apoptosome complex with cytochrome c and APAF-1 and leads to apoptosis through activation of caspase-3. Aminoglycosides activate caspases in auditory structures conversely, inhibition of caspase activity successfully blocks neomycin-induced vestibulotoxicity. In contrast, apoptotic markers were essentially absent in a mouse model of chronic kanamycin ototoxicity where death of auditory sensory cells ensued via cathepsins. The activation of cathepsin D was accompanied by the nuclear translocation of endonuclease G, necrotic cleavage of PARP, and activation of p,-calpain, all facets of necrotic cell death. 

Restriction endonucleases require the presence of Mg2+ for activity. The quench buffer contains EDTA, which complexes transition metal ions in the solution. The metal ions are no longer available for binding by the nuclease molecules and enzyme activity is inhibited. 

The existence of a deoxyribonuclease in E. coli bound to an inhibitory RNA was first suggested by Kozloff (3< ) who found that the DNase activity of freshly prepared extracts could be markedly enhanced by pretreatment with ribonuclease. The enzyme was subsequently purified and freed of inhibitor (39). The purified enzyme termed endonuclease I could, in turn, be competitively inhibited by a variety of RNA s including transfer RNA, and Ri values as low as 10-8 M (nucleotide) have been observed (40). Examination of various purified RNA species and synthetic polyribonucleotides for their inhibitory activity has led... 

Sikora E, Bielak-Zmijewska A, Magalska A, Piwocka K, Mosieniak G, Kalinowska M, Widlak P, Cymerman IA, Bujnicki JM. 2006. Curcumin induces caspase-3-dependent apoptotic pathway but inhibits DNA fragmentation factor 40/caspase-activated DNase endonuclease in human Jurkat cells. Mol Cancer Ther 5 927-934. 

This type of reaction inhibits the repair by endonuclease III from E. coli, and Lys-120 is responsible for this cross-linking reaction. Under the conditions of these experiments, the cross-linking efficiency is 20%. It is expected that such cross-linking reactions are more general and that more examples will be detected. 

Henricksen, L.A., Tom, S., Liu, Y. and Bambara, R.A. (2000) Inhibition of flap endonuclease 1 by flap secondary structure and relevance to repeat sequence expansion. J. Biol. Chem., 275,16420-16427. 

R. J. Rodriguez (1993). Polyphosphate present in DNA preparation from filamentous fungal species of Colleotrichum inhibits restriction endonucleases and other enzymes. Anal. Biochem., 209, 291— 297. 

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