A Comparison of the Light and Dark Portions of a Striated Muscle

SUMMARY— The levels of physio'ogically related muscle constituents were determined in the light (white) and dark (red) portions of a striated muscle from the pig (SW domcsticus). Myoglobin level, percent red fibers and succinic dehydrogenase activity were two‐fold higher in the semitendinosus dark portion whereas ADP and inorganic phosphate levels were similar in both portions. Phosphorus levels were higher and sodium levels lower in the semitendinosus light portion than in the semitendinosus dark portion. Zinc and iron contents were greater in the dark portion than in the light portion; calcium, nickel, boron and potassium levels were similar in both portions. The semitendinosus light portion also had more lipid and more sarcoplasmic nitrogen than did the semitendinosus dark portion. These data suggest that the light (white) and dark (red) portions within the semitendinosus have physio‐chemical properties similar to uniformly white and uniformly red muscles, respectively.