A comparison of order and orientation of crossbridges in rigor and relaxed muscle fibres using fluorescence polarization.

Information has been obtained concerning the spatial disposition of the fluorescent reagent 5-(iodoacetamidoethylaminonaphthalene)-1-sulphonic acid bound covalently to muscle proteins in chemically skinned fibres of rabbit psoas muscle, using a novel time-gated fluorescence detection system to reject scattered incident light selectively. The results are consistent with a model of muscle crossbridge organization in which a particular crossbridge axial angle is strongly favoured in the rigor state. The structure in relaxation is less well ordered, but the favoured axial angle appears to be very close to that in rigor. This conclusion does not depend upon which of the models of crossbridge organization considered here is chosen, and is essentially unchanged if results obtained using a different fluorophore are analysed in the same way.