The amino acid sequence and oligosaccharide distribution for the haemagglutinin from the early Hong Kong influenza virus A/Aichi/2/68 (X-31) was investigated. The two polypeptide chains, HA1 and HA2, were fragmented by CNBr and enzymic digestion, and the amino acid sequence of each small peptide was deduced by comparing its chromatographic behaviour, electrophoretic mobility, amino acid composition and N-terminus with that of the corresponding peptide of the haemagglutinin of known structure from the influenza-virus variant A/Memphis/102/72. Those peptides in which changes were detected were sequenced fully. The complete amino acid sequence of the haemagglutinin HA1 chain (328 residues) and 188 of the 221 residues of the HA2 chain were established by this approach, and revealed only twelve differences between the amino acid sequences of variant-A/Aichi/68 and -A/Memphis/72 haemagglutinins. These occurred at positions 2, 3, 122, 144, 155, 158, 188, 207, 242 and 275 in the HA1 chain and 150 and 216 in the HA2 chain. The highly aggregated hydrophobic region (residues 180-121) near the C-terminal end of the HA2 chain was not resolved by peptide sequencing. The oligosaccharide distribution in variant-A/Aichi/68 haemagglutinin was identical with that found in that of A/Memphis/72, with sugar units attached at asparagine residues 8, 22 38, 81, 165 and 285 in the HA1 chain and 154 on the HA2 chain. The monosaccharide compositions of the individual carbohydrate units on variant-A/Aichi/68 haemagglutinin differed from those of the corresponding units in variant-A/Memphis/72 haemagglutinin, and evidence was found for heterogeneity in the oligosaccharide units attached at single glycosylation sites.

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