Comparison of HA subtypes that caused pandemics.

<p>(A) Cleavage site mimetic peptide representative of H1N1 strains was monitored for cleavage by the indicated proteases. Red letter in the peptide sequence emphasizes a different amino acid compared to the cleavage sequence of the H1 isolate A/WSN/33 (B). (C) and (D) display cleavage assays of peptide mimics representative for H2N2/H2N6 and H3N2 strains, respectively. RFU—relative fluorescence units.