title: Identification of a major serum DNA-binding protein as factor B of the alternative complement pathway.
abstract: One of the major proteins in human serum capable of binding DNA has been shown to be factor B of the alternative pathway of complement activation. This protein, designated DNA-binding protein-2 (DBP-2), is recognized by antisera directed against both factor B and its activated form, fragment Bb. Its m.w., charge microheterogeneity, and amino acid composition correspond closely with reported values for those properties of factor B. A radioimmunoassay was used to estimate the serum concentration of DBP-2 at 266 +/- 83 microgram/ml, which also corresponds with the level of factor B normally present in the serum. DBP-2 functions as factor B in the activation of factor B-depleted serum. Limited proteolytic treatment of DBP-2 produced a fragment pattern resembling that of factor B both in the m.w. of the fragments and their electrophoretic mobilities. By means of DNA affinity chromatography of the fragments produced by trypsinization, the DNA-binding domain of DBP-2 was localized.
mesh_terms: D000595:Amino Acid Sequence; D055598:Chemical Phenomena; D002621:Chemistry; D003167:Complement Activation; D011415:Complement Factor B / Q000378:metabolism*; D003170:Complement Pathway, Alternative; D004247:DNA / Q000378:metabolism*; D004792:Enzyme Precursors / Q000378:metabolism*; D005260:Female; D006461:Hemolysis; D006801:Humans; D007106:Immune Sera / Q000494:pharmacology; D008297:Male; D008970:Molecular Weight; D010447:Peptide Hydrolases / Q000494:pharmacology; D011485:Protein Binding; D011863:Radioimmunoassay; D014357:Trypsin / Q000494:pharmacology
chemical_list: D004792:Enzyme Precursors; D007106:Immune Sera; D004247:DNA; D010447:Peptide Hydrolases; D014357:Trypsin; D011415:Complement Factor B