title: Evidence for histidine residues in the immunoglobulin-binding site of human Clq.
abstract: The immunoglobulin-binding activity of subcomponent Clq of human complement is lost following treatment with diethylpyrocarbonate; the inactivation showed first-order kinetics with respect to time and modifier concentration. Soluble IgG oligomers protected Clq against diethylpyrocarbonate modification. Treatment of modified Clq with hydroxylamine resulted in an 85% recovery of its ability to bind to aggregated immunoglobulin. The inactivation process was associated with modification of 12.1 +/- 0.7 histidine residues per Clq molecule. These data are consistent with the presence of histidine residues in the immunoglobulin-binding sites of Clq; these residues may participate in ionic interactions with the carboxyl groups known to be in the Clq binding site of IgG.
mesh_terms: D055598:Chemical Phenomena; D002621:Chemistry; D003166:Complement Activating Enzymes / Q000302:isolation & purification*; D015922:Complement C1q; D004047:Diethyl Pyrocarbonate / Q000494:pharmacology; D006639:Histidine / Q000302:isolation & purification*; D006801:Humans; D017452:Receptors, IgG; D011971:Receptors, Immunologic; D013696:Temperature
chemical_list: D017452:Receptors, IgG; D011971:Receptors, Immunologic; D006639:Histidine; D015922:Complement C1q; D003166:Complement Activating Enzymes; D004047:Diethyl Pyrocarbonate