Rapid purification of topoisomerase I from human breast cancer cells by high-performance liquid chromatography

Abstract

The DNA regulatory enzyme topoisomerase I (TpI) from human breast cancer cells has been analyzed by high-performance liquid chromatography (HPLC) for the first time. Cells were homogenized in Tris buffer and TpI activity was extracted with 0.5 M sodium chloride. Negatively supercoiled plasmid pBR322 was used as the substrate to monitor TpI activity, as judged by relaxed products, analyzed on 1% agarose gels. HPLC in the anion-exchange mode (HPIEC) provided an approximately 6-fold purification of the enzyme. Enhanced purification was subsequently obtained by chromatography of a HPIEC eluate on size-exclusion columns (30- to 60-fold). Recovery of TpI from size-exclusion columns, whether used in multistep analysis or as the first step, was dependent on inclusion of organic solvent, 1-propanol (0.5%, v/v), in the mobile phase. Marked resolution of TpI activity was observed with HPIEC on a SynChrom CM-300 column. Enzyme activity was noted in the void volume, at 150–200 m M phosphate and at 250–350 m M phosphate. TpI purification was 10- and 120-fold in the latter two peaks, respectively. Silver-stained polyacrylamide gels of TpI-containing activity, eluted from a CM-300 column, showed considerable purification of all but the void volume fraction. A distinct protein band at approximately 88–90 kD was seen in the peak eluted from the CM-300 column with 250–350 m M phosphate. These results indicate that HPLC is useful for rapid purification of the labile enzyme, TpI, in the analysis of its structure—function relationship.