Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.22.1 (DNase II)
 429 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The nature of the endonucleases responsible for DNA fragmentation in apoptosis has not yet been clearly defined. The intracellular acidity has been known to greatly affect apoptosis probably by affecting the activity of the endonucleases. In this study, the implication of pH in the apoptosis was investigated through the use of human HL-60 leukemia cells. The cells were incubated in media with different pH ranging from 3.5 to 7.5 for 4 hrs and the mode of cell death was investigated. The trypan blue exclusion assay showed that close to 25% and 90% of the cells were dead when incubated in pH 6.4 and pH 5.0 media, respectively. The agarose gel electrophoresis of DNA demonstrated that significant DNA fragmentation occurred in the HL-60 cells incubated in the pH 6.2-6.4 media for 4 hr indicating cell death by apoptosis. The electron microscopy study also demonstrated that many of the cells incubated in the pH 6.4 medium were in the process of apoptosis while the cells maintained in the pH 5.0 medium were dying by necrosis. The intracellular pH (pHi) of HL-60 cells was 6.6-6.9 when the extracellular pH (pHe) was 6.2-6.4. These results demonstrated that DNase I which has a maximal endonuclease activity near pH 7.0 may be responsible for the apoptosis accompanied by DNA fragmentation in HL-60 cells in the pH 6.4 medium. This observation is at variance with the previous reports that DNase II mediate the DNA fragmentation in apoptosis. The cell death at extremely low pH (pH 5.0) appeared to be due mainly to necrosis.
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PMID:Effects of intracellular pH on apoptosis in HL-60 human leukemia cells. 859 48

The effect of ionic strength of the reaction medium on the pH optimum, specificity, and mechanism of action of the acid DNase isolated from mature eggs of the sea urchin Strongylocentrotus intermedius was studied. Changes in ionic strength of the reaction medium caused a displacement of the pH optimum of the enzyme to acidity or alkalinity. The region and range of this displacement depended on the buffer used and on the substrate structure. For single-stranded, duplex, and supercoiled forms of DNA, the pH optimum displacements were 1.0, 1.4, and 2.0 pH units, respectively. The pH optimum displacement changed the mechanism of action of the enzyme. Under optimum pH conditions, the enzyme cleaved supercoiled DNA only by the double-hit mechanism, and fragments of duplex DNA resulted due to the coincidence of breaks in opposite chains. On pH displacement to acidity, the enzyme acted by the mixed mechanism (single- and double-hit). And the quantitative ratio of products of the enzymatic hydrolysis of supercoiled DNA was significantly changed depending on the pH displacement to acidity or to alkalinity. The findings are explained by the effect of salt-dependent electrostatic interactions during the formation of a nonspecific DNA-enzyme complex.
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PMID:Effect of ionic strength on the pH optimum, specificity, and mechanism of action of acid DNase from mature eggs of the sea urchin Strongylocentrotus intermedius. 1100 89