title: Evidence for arginine residues in the immunoglobulin-binding sites of human Clq.
abstract: The immune complex binding activity of human Clq was lost following treatment of the protein with the arginine-selective reagents cyclohexane 1,2-dione and phenylglyoxal. Both inactivations followed pseudo-first-order kinetics. The affinity of Clq for immune complexes was reduced 7-fold following cyclohexane-1,2-dione treatment, and could be substantially restored by treatment of the modified protein with hydroxylamine. Heat-aggregated IgG protected Clq against inactivation by both reagents. Incorporation of 25 molecules of [7-14C]phenylglyoxal per Clq molecule completely inactivated the protein. These data are consistent with the presence of arginyl residues in the immunoglobulin recognition sites of human Clq.
mesh_terms: D000936:Antigen-Antibody Complex; D001120:Arginine / Q000037:antagonists & inhibitors / Q000378:metabolism*; D001665:Binding Sites; D001667:Binding, Competitive; D002021:Buffers; D003166:Complement Activating Enzymes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015922:Complement C1q; D003512:Cyclohexanones / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D010658:Phenylglyoxal / Q000494:pharmacology
chemical_list: D000936:Antigen-Antibody Complex; D002021:Buffers; D003512:Cyclohexanones; C018031:1,2-cyclohexanedione; D015922:Complement C1q; D001120:Arginine; D003166:Complement Activating Enzymes; D010658:Phenylglyoxal