The activity of commercial DNase I and DNase II after in vitro treatment with NO donor (SNP) or peroxynitrite. Purified enzymes DNase I (E.C. 184.108.40.206) and DNase II (E.C. 220.127.116.11) were dissolved in physiological saline solution. Hepatocytes, isolated from 8 Male Sprague-Dawley rats, were dissolved in a physiological saline solution in a concentration of approximately 108 cells/ml. They were divided into seven groups (each comprising 8 samples) exposed to either SNP (0.1, 1 and 10 mmol) or peroxynitrite (0.03, 0.3 and 3 mmol). The reducing agent (cysteine 1 mmol) was added to SNP to induce in vitro NO release . The activity of alkaline and acid-DNase was measured by the methods of Bartholeyns et al.  and acid soluble nucleotides were determined spectrophotometrically at 260 nm. The defined units for purified DNase I and DNase II (increase in absorbance of 0.001/min in a sample containing 0.132 mg DNA, pH 7.4 or pH 5 and 3 ml of reaction mixture) were obtained from the Sigma catalogue label. Data (n = 8) in graph is putted as: Mean + SD.