Characterization of carbohydrate chains of C1-inhibitor and of desialylated C1-inhibitor.

Carbohydrate chains of C1-inhibitor were identified with a binding assay using different lectins. Lectins from Sambucus nigra (SNA) and Maackia amurensis (MAA) that are specific for sialic acids bound to C1-inhibitor. Lectin from Datura stramonium (DSA) reacted also with the inhibitor indicating complex and hybrid sugar structures. C1-inhibitor was enzymatically desialylated and reexamined for lectin binding. SNA and MAA did not react anymore, but in addition to DSA, peanut agglutinin, which can bind to carbohydrate chains after sialic acids are removed, bound to desialylated C1-inhibitor. C1-inhibitor contains about 30 sialic acid residues per molecule. SDS-polyacrylamide gel electrophoresis showed that desialylated C1-inhibitor had a faster mobility than native C1-inhibitor. The N-terminal sequence of desialylated C1-inhibitor was the same as of native C1-inhibitor and no change in the inhibition of human plasma kallikrein was observed.