Open AccessComparison of biochemical properties of DNA‐topoisomerase I from normal and regenerating liver
Author(s) -
TOURNIER MarieFrançoise,
SOBCZAK Joëlle,
NECHAUD Béatrice,
DUGUET Michel
Publication year - 1992
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1992.tb17429.x
Subject(s) - topoisomerase , chromatin , dephosphorylation , biochemistry , enzyme , liver regeneration , phosphatase , dna , biology , phosphorylation , microbiology and biotechnology , alkaline phosphatase , chemistry , regeneration (biology)
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 p I 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.