BEHAVIOR OF N-PHENYLMALEIMIDE-REACTED MUSCLE-FIBERS IN MAGNESIUM-FREERIGOR SOLUTION

Using x-ray diffraction and mechanical stiffness, the response of N-ph enylmaleimide (NPM)-reacted crossbridges to solutions containing diffe rent amounts of ATP and Mg2+ has been studied, In relaxing solution co ntaining greater than millimolar amounts of ATP and Mg2+, NPM-treated muscle fibers give x-ray diffraction patterns and stiffness records, w hich are nearly indistinguishable from those of untreated relaxed fibe rs. In a solution devoid of added ATP, but with Mg2+ (rigor(+ Mg) solu tion), the muscle fibers still give x-ray diffraction patterns and mec hanical responses characteristic of relaxed muscle. The new finding re ported here is that in a solution devoid of both ATP and Mg2+ (rigor(- Mg) solution containing EDTA with no added ATP), NPM-reacted cross-bri dges do give rigor-like behavior. This is the first report that NPM-re acted cross-bridges, at least in the presence of EDTA, are capable of going into a strongly binding conformation.