Fig. 3.
The effect of selective actin extraction and titin digestion on passive mechanical properties of HH myofibrils. (A) Average Vp (release step, 2.35- to 2.0-μm SL) increased immediately when gelsolin fragment was added to the relaxing buffer to extract actin (n = 3 myofibrils; means ± SD). Titin proteolysis (by adding low doses of trypsin to the buffer) reduced the average Vp of actin-extracted myofibril within minutes (release step, 2.35- to 2.0-μm SL). (B) Polyacrylamide gel was used to show titin degradation in HH myofibrils on mild trypsin treatment. T2 and T3 are proteolysis products. (C) PT of intact and actin-extracted myofibrils during stretch from a 1.85- to 2.40-μm SL (stretch time, 0.5 s). The data represent average tension of three different myofibrils at each experimental condition. (D) A half-logarithmic representation of the average Vp before and after actin extraction for different release amplitudes from a 2.3-μm SL. Curves are best fits to data points with single-exponential decay function.