The structure of influenza viruses: II. C-terminal amino acid analyses

Reaction of influenza B virus (LEE strain) with carboxypeptidase resulted in the rapid and simultaneous release of leucine and tyrosine in the approximate molar ratio of 1.5:1, followed by smaller amounts of other, unidentified amino acids. This result was obtained only when the virus was denatured with formamide or cuprammonium sulphite; practically no amino acids were released from native virus under similar conditions of digestion.Leucine and tyrosine were released only from the fraction of cuprammonium sulphite-treated LEE virus previously shown to be lacking N-terminal aspartic acid. The protein which possessed an N-terminal aspartic acid residue was much less susceptible to the action of carboxypeptidase, and its C-terminal residue was not identified. Fractions obtained by electrophoresis of dodecyl sulphate-disrupted LEE virus were reacted with carboxypeptidase. Equimolar amounts of leucine and tyrosine were split off from the fastest fraction, but from the slowest, the ratio of leucine to tyrosine released was 7.5:1. These results suggest that particles of LEE virus contain at least three different kinds of polypeptide chains.Reaction with carboxypeptidase of the MEL, BEL, and PR8 strains of influenza A virus (denatured by cuprammonium sulphite), resulted in the slow and simultaneous release of about five amino acids from each strain. None of these could be unequivocally identified as C-terminal.