Purification and Identification of a Human‐Serum DNA‐Binding Protein Associated with Malignant Diseases

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Abstract
A malignancy associated human serum DNA-binding protein (C3DP protein), which was previously detected using dodecylsulfate gel electrophoresis, was purified and characterized. This protein was isolated from human fetal cord serum by DNA-cellulose affinity chromatography, ammonium sulfate fractionation, DEAE-cellulose chromatography and Sephadex gel filtration. The MW of purified C3DP protein was 135,000 by ultracentrifugation, gel filtration and dodecylsulfate gel electrophoresis. Dodecylsulfate gel electrophoresis following disulfide bond reduction revealed that this protein is composed of 3 subunits having MW of 74,000, 40,000 and 22,000. Carbohydrate was attached to the 74,000 and 22,000 MW components. Immunochemical studies revealed that the C3DP protein is a fragment of human complement component C3, which closely resembles C3c.