Carp myogens of white and red muscles. Properties and amino acid composition of the main low-molecular-weight components of white muscle

1. The three main components of the 1·5–2s ultracentrifugal peak of carp myogen (white muscle) have been isolated by ammonium sulphate fractionation and zone electrophoresis, and crystallized. 2. The molecular weights of these three proteins were determined by sedimentation and diffusion, by the Archibald method and by amino acid analysis, and found to lie between 9000 and 13000. 3. Their complete amino acid compositions were determined by column chromatography and by their ultraviolet spectra. Both methods revealed abnormal compositions, including the absence of tryptophan and methionine and the presence of large amounts of phenylalanine. At most 1 residue each of tyrosine, cysteine, proline, arginine and histidine was found/molecule. 4. The specific viscosity of component 3 was lower than that of other small globular proteins described so far, a fact that suggests that these proteins approximate more closely to the ideal case of the spherical protein molecule. Also, the presence of a single residue of several amino acids, the absence of disulphide bonds, and the apparent reversibility of denaturation by urea of component 3 suggest that the study of these molecules could provide new information on the structure of proteins.