Functional unit (FU) RtH2-e from Rapana thomasiana hemocyanin (He) was degraded into small fragments with chymotrypsin. The glycopeptides were separated from the non-glycosylated peptides by chromatography on Concanavalin-A-Sepharose and characterized by mass spectrometry. The glycan part of tile glycopeptides (all with common peptide stretch of 14 amino acids) consists of the classical trimannosyl-N,N-diacetylchitobiose core for N-glycosylation, predominantly extended with a unique tetrasaccharide that is branched on fucose. In inhibition ELISA experiments, the glycopeptides interfered in the complex formation between FU RtH2-e and rabbit antibodies against Rapana He (about 30% of inhibition). The inhibition also was retained after treatment of the glycopeptides with pronase in order to completely destroy the peptide part. The inhibitory effect of tile non-glycosylated peptides, on the other hand, was very low. This study thus demonstrates that the glycans attached to FU RtH2-e contribute to the antigenicity of Rapana He. (c) 2007 Elsevier Inc. All rights reserved.