Figure 8.

The C-state rate of Tn dissociation is cooperative with calcium and strong cross-bridges. Labeled Tn exchange was done as for Figure 2, and presented as in Figure 6. The non-overlap region is noted by a red rectangle outline. The rate of Tn dissociation, at sub-maximal calcium (pCa 6.1 to 5.8, the region of cooperative activation of ATPase activity) was not uniform along the length of the non-overlap thin filament at 16 min. A region of enhanced exchange occurred just proximal to the overlap region, and depending on pCa, slowed from the proximal overlap region towards the Z-line. After extensive exchange (1024 min), the intensity was mostly equal in the non-overlap and overlap region except for pCa 9. A subtle sub-region of extra Tn exchange was apparent at pCa 4, just proximal to the Z-line. This was also evident for TnCIT and TnT myofibrils at pCa 4 (Figure 5(a)).