title: The interaction of 1-anilino-8-naphthalene sulphonate with human C1q.
abstract: C1q has 12 binding sites for 1-anilino-8-naphthalene sulphonate (ANS), two per peripheral subunit. This number increases to 18 upon weak-acid-induced conformational transition in the globular heads. One ANS binding site is present in each C gamma 2 domain of human IgG. ANS is bound by C1q with a higher affinity (Ka = 2.07 X 10(6) M-1) than by the Fc fragment (Ka = 9.07 X 10(4) M-1) of human IgGl. Hence the inhibitory capacity of C1q binding to IgG immune complexes of ANS probably reflects its preferential binding to the globular heads of C1q. The characteristics of ANS-C1q binding may in part explain the hydrophobic component of the C1q-IgG interaction. It is suggested that an ionic-hydrophobic two-step process is involved in the contact between C1q and IgG.
mesh_terms: D000817:Anilino Naphthalenesulfonates; D001665:Binding Sites; D055598:Chemical Phenomena; D002621:Chemistry; D003166:Complement Activating Enzymes / Q000302:isolation & purification; D015922:Complement C1q; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007141:Immunoglobulin Fc Fragments; D003012:Microbial Collagenase; D010434:Pepsin A; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence
chemical_list: D000817:Anilino Naphthalenesulfonates; D007141:Immunoglobulin Fc Fragments; C027132:1-anilino-8-naphthalenesulfonate; D015922:Complement C1q; D003166:Complement Activating Enzymes; D010434:Pepsin A; D003012:Microbial Collagenase