Acta Biochimica et Biophysica 10. (1975)

1975 / 3. szám - Belágyi, J.: Orientation Dependence in the Epr Spectra of Spin Labels in Glycerinated Muscle Fibres

Acta Biochim. et Biophys. Acad. Sei. Hung. Vol. 10 (3), pp. 233— 242 (1975) Orientation Dependence in the Epr Spectra of Spin Labels in Glycerinated Muscle Fibres J. Belágyi Central Laboratory, Medical University, Pécs, Hungary (Received October 3, 1974) Glycerinated muscle fibres labelled with a set of five-membered maleimide spin labels revealed a complex type epr spectra, which showed a reduced rate of anisotropic motion. The spectra can be interpreted in terms of the ratio of the two down-field peaks and of the hyperfine coupling constant. The spectra clearly indicated that the preferred orientation of the 2pn molecular orbital of the odd electron is perpendicular rather than parallel to the long axis of the muscle fibres. Increasing chain length between the maleimide ring and pyrrolidine nitroxide ring reduces the orientational anisotropy. Thermal dénaturation destroys the orientation dependence of the epr spectra of spin labels. The Mg-ATP induced shortening of the fibres influ­ences the spectral parameters. The fibres which had been contracted showed a modified orientation dependence of epr spectra. Introduction Nitroxide spin labelling proved to be a useful tool in studies on contractile proteins of muscle and model systems (Seidel et al., 1970; Stone et al., 1970; Seidel, Gergely, 1971, 1973; Tokiwa, 1971). The electron paramagnetic resonance (epr) spectrum is sensitive to the orientation of spin labels with respect to the labo­ratory magnetic field and depends on the rotational mobility of the spin labels (Hamilton, McConnel, 1968; Griffith, Waggoner, 1969; McConnell, McFarland, 1970). The pronounced anisotropy of the striated muscle and glycerinated muscle fibres reflects an arrangement of the molecular structure which plays an important role in physiological processes (Ernst, 1963). With a structural probe such as spin label it may be possible to test the molecular structure around the label and to study the orientation dependence which is evoked by the anisotropic distributions of label orientation. Cooke and Morales (1969) were the first to study the epr spectrum on glycerinated fibres labelled with six-membered maleimide spin label. It has been the aim of the present work to investigate the orientation depen­dence of epr spectrum on glycerinated muscle fibres with SH-directed spin labels in order to obtain information on the local order of the contractile system and to look for possible changes after Mg-ATP induced shortening and thermal déna­turation. We confirm and extend the earlier experiments and try to give a possible interpretation. Acta Biochimica et Biophysica Academiae Scientiarum Hungaricae 10, 1975

Next