The Localization of the Adenylic Acids in Striated Muscle‐Fibres

Summary. Ultra‐violet absorption‐spectra have been measured of individual isotropic and anisotropic segments in striated muscle‐fibres from insects. By means of comparisons with ultra‐violet micro‐photographs it is shown to be probable that the results obtained in this way are applicable to striated musculature in general. The absorption‐curves show that the main part of the adenine derivatives (adenylic acid and adenyl‐pyrophosphoric acid) in the resting muscle are localized in I. These segments seem to have their main function as the seat of chemical energetic processes while A is the seat of the contractile elements. From observations on fatigued muscle‐fibres one deduces that energy is transferred from I to A by adenyl‐pyrophosphate whose energy is released by the phosphatase that is bound to the myosin. The background to the striation of the muscle‐fibres thus seems to be a differentiation of contractile parts and chemically‐working parts respectively. The transport of energy from the latter to the former is performed by adenyl‐pyrophosphoric acid. The work has been supported by funds from the Rockefeller Foundation and the foundation “Thérèse oeh Johan. Anderssons minne.”