Some scleroderma patients produce high titer antibody directed against human topoisomerase I (Shero et al., 1986).  The immunoglobulin fraction was purified from these patients and shown to react specifically with the 100 kDa form of Topo I using Western blotting.  The immune complexes produced with this reagent will bind [125I]-protein A.  When intact topoisomerase I is used, a single polypeptide of 100 kDa was detected; however, sub-bands produced by proteolysis will also bind this reagent, as expected.  The antibody is particularly useful as a Western blotting probe and can be used at high dilutions (>1:5,000).  Cross reactivity of this antibody with other species has been demonstrated (with calf thymus).  Important note about product use: Human topoisomerase I undergoes spontaneous degradation especially with repeat freezing/thawing. The activity of the enzyme is not affected significantly; however, sub-bands may be detectable in Western blotting experiments. This antibody may be used in immunoprecipitation experiments.