POLARIZATION OF TRYPTOPHAN FLUORESCENCE IN MUSCLE

The polarization of tryptophan fluorescence from glycerinated rabbit muscle was examined as a possible indicator of changes in orientation or conformation of muscle proteins. The fluorescence was excited at 300 mμ and was observed on axis after removing the exciting light with filters. When rigor muscle fibers were excited the polarization, p, was ~0.32 when the exciting light was polarized with the electric vector parallel to the muscle fiber axis, p‖, and ~0.08 when it was polarized with the electric vector perpendicular to the fiber axis, p┴. This anisotropy in p is associated with the structure of the muscle and is not due to dichroism in the usual sense. Relaxation of the muscle brought about by the addition of adenosine triphosphate (1 mm or higher) in a solution containing ethylene glycol bis(β-aminoethyl ether) N,N-tetraacetic acid plus magnesium ions caused a reversible increase in p┴ from ~0.08 to ~0.125 and no obvious change in P‖. Isometric contraction evoked by ATP and calcium ions produced intermediate values, viz., ~0.10. High concentrations of glycerol (50-95 %, v/v) also caused an increase in p┴ while having little effect on p‖ while pH, KCl concentration, D2O, and several nucleotides and polyphosphates had little observable effect on either p‖ or p┴. We conclude that p┴ is a sensitive indicator when different functional states are imposed on muscle either by the binding of adenosine triphosphate or by the activation of adenosine triphosphate hydrolysis by calcium ions. We favor the view that the change in p┴ reflects changes in the average orientation of some tryptophan-containing element of muscle. © 1969, American Chemical Society. All rights reserved.