Structures of Sugar Chains of the Third Component of Human Complement

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Abstract
Human C3, the third component of human complement, contained mannose andN-acetylglucosamine as sugar components. The sugar chains were liberated from the polypeptide chains by hydrazinolysis, and the free amino groups were N-acety-lated. The reducing end residues of the sugar chains thus obtained were tagged with 2-aminopyridine, and the pyridylamino (PA-) derivatives of sugar chains were separated by high-performance liquid chromatography. The structures of purified PA-sugar chains were analyzed by a combination of stepwise exoglycosidase digestions, size determination by paper electrophoresis, methylation analysis, Smith degradation, and partial acetolysis. These results showed that C3 contained two high-mannose type sugar chains ranging from Man5GIcNAc2 to Man9GlcNAc2. Analyses of the sugar chains of α- and β-chains of C3 indicated that the α-chain contained mainly Man8GIcNAc2 and Man9GlcNAc2, while the β-chain contained mainly Man6GlcNAc2 and Man6GlcNac2.