Comparison of biochemical properties of DNA-topoisomerase I from normal and regenerating liver.
Biochemical properties of topoisomerase I from normal and regenerating rat liver were analysed using crude or fractionated nuclear extracts. We could not detect significative change in topoisomerase I content or activity (magnesium stimulation and inhibition by ATP) during the course of liver regeneration. Topoisomerase I can be resolved into two species of 97 kDa and 100 kDa, with the same pI of 8.2-8.6 as shown by two dimensional gel electrophoresis. The two polypeptides contained a non-phosphorylated precursor and others forms with variable degrees of phosphorylation. In-vitro dephosphorylation with alkaline phosphatase leads to the disappearance of the phosphorylated forms and inactivation of the enzyme. The affinity of topoisomerase I for chromatin (measured by salt elution) differs markedly between normal and regenerating liver: nearly 50% of topoisomerase I remained bound to the chromatin from normal liver at 250 mM NaCl whereas it was completely eluted from 24-h-regenerating-liver nuclei. The biological significance of these results is discussed.
Tournier
M F
MF
Laboratoire d'Enzymologie des acides nucléiques, Université Pierre et Marie Curie, Paris, France.
Sobczak
J
J
de Nechaud
B
B
Duguet
M
M
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002843:Chromatin / Q000378:metabolism; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D008099:Liver / Q000201:enzymology*; D008115:Liver Regeneration; D008297:Male; D010766:Phosphorylation; D051381:Rats; D017208:Rats, Wistar; D013379:Substrate Specificity
D002843:Chromatin; D000255:Adenosine Triphosphate; D004264:DNA Topoisomerases, Type I