title: Structure-function relations in the third component of human complement (C3)-I. Hydrophobic site.
abstract: Charge shift electrophoresis and crossed hydrophobic interaction immuno-electrophoresis were used to demonstrate the presence of hydrophobic sites in the human C3 molecule. C3b and C3d were true amphiphilic proteins that could bind to hydrophobic surfaces. To the contrary, native C3, that presented the characteristics of amphiphilic proteins upon charge shift electrophoresis, did not bind to hydrophobic surfaces. These results suggested that the hydrophobic sites were located in the internal part of the C3 molecule and they were exposed in the external part when C3 was activated. The action of chaotropes on C3 was studied in detail and showed that the hydrophobic sites protected the thiolester bond (present in the labile site) from hydrolysis by water and thereby preserved the biological properties of native C3.
mesh_terms: D001665:Binding Sites; D002942:Circular Dichroism; D003176:Complement C3; D003902:Detergents; D004586:Electrophoresis; D006461:Hemolysis; D006801:Humans; D010446:Peptide Fragments; D011487:Protein Conformation; D011489:Protein Denaturation; D012995:Solubility; D013329:Structure-Activity Relationship; D013696:Temperature
chemical_list: D003176:Complement C3; D003902:Detergents; D010446:Peptide Fragments