Laser Raman scattering. A molecular probe of the contractile state of intact single muscle fibers

The 500 to 1,800-cm-1 region of the Raman spectra of intact single muscle fibers from the giant barnacle are dominated by bands caused by the protein component of the fibers. The frequency and the intensity of the conformationally sensitive bands indicate that the contractile proteins adopt a predominantly alpha-helical structure and are not affected when the contractile state of the fibers is changed from relaxed to contracted by addition of ATP and Ca. However, the contraction induces a decrease of the scattering intensity of some of the Raman bands caused by the acidic and tryptophan side chains, showing that these amino acids are involved during the generation of tension.