ON THE USE OF ZN2+ TO DISCRIMINATE ENDONUCLEASES ACTIVATED DURING APOPTOSIS

One approach to discriminate among specific DNases in apoptosis is to use inhibitors specific for each endonuclease. Zn2+ is known to inhibi t Ca2+ and Mg2+-dependent endonuclease enzymatic activities during apo ptosis. Acidic DNases were thought to be insensitive to Zn2+. In this paper, we analyse the effects of Zn2+ on activity of DNase II, either purified or in nuclei from lens fiber cells. These cells follow a phys iological nuclear degeneration with DNase II accumulation in their nuc lei. We show that Zn2+ is able to inhibit also this acidic endonucleas e at a concentration of 1-6 mM. At a higher concentration of Zn2+, DNA is extensively degraded during the assay, masking the inhibition of t he enzyme. This DNA degradation in the presence of Zn2+ has led to an overestimation of the activity of DNase II in studies of apoptosis. He nce, Zn2+ cannot be used to specifically identify one endonuclease amo ng the different DNases involved in nuclear degradation during program med cell death.