Figure 5. Structural responses following photo-liberation of 1.1 mM ATP from 10 mM DMB-caged ATP in the presence of Ca²⁺ in single partially EDC cross-linked frog muscle fibres at 5–6 °C.

A, typical sarcomere length record; B, averaged tension transients; C, the intensity of the equatorial X-ray reflections, I_1,0 (⋄) and I_1,1 (□); D, the intensity of the meridional reflection at (14.5 nm)⁻¹, I_M3; E, the intensity of the myosin-actin layer line, I_LL1. The tension trace shown in B was averaged from 69 experiments in 18 muscle fibres; the X-ray data were collected from 75 experiments in the same fibres. The curves in C-E are exponential fits to the data (see legend to Fig. 4 and text). The vertical dotted lines show where the time scale was changed. In D and E, the 1 ms time frames were averaged into 5 ms time bins during the first 50 ms, for clarity. The averaged values were assigned a time corresponding to the centre of the time interval. In E, the intensity I_LL1 was determined by radial off-meridional integration from (35 nm)⁻¹ to (8 nm)⁻¹ and with subsequent meridional integration and linear background subtraction, so both the first actin layer line at ≈(37 nm)⁻¹ and the first myosin layer line at ≈(43 nm)⁻¹ contributed to I_LL1, although the first myosin layer line remained constant at 7 % of the total intensity.