Isolation from trout liver of a methionine-containing H1 subfraction, THImet

A trout H1 subfraction, THImet, which contains one residue of methionine and a blocked N-terminal amino acid, has been isolated from trout liver. Cyanogen bromide cleavage of THImet and amino acid analysis and polyacrylamide gel electrophoresis of the cleavage products show that it contains a residue of methionine at about the same distance from the N terminus as mammalian H1o and avian H5. THImet is shown to be similar to, but not identical with, the protein derived from trout erythrocytes generally accepted as the equivalent in fish of avian H5.