Figure 5.
MLC composition and actin filament gliding velocity of myosin extracted from individual type-I M. soleus fibers. (A) Example of MLC SDS-PAGE analysis of individual type-I M. soleus fibers. For each fiber, the respective relative content of MLC1sa (upper band) versus MLC1sb/v (lower band) was determined by densitometric analysis of the SyproRuby-stained 15% SDS-PAGE gel. Note that all tested M. soleus fibers contained both ELC isoforms; the majority showed a higher content of MLC1sa, which was not detected in the control ventricular myosin. (B) Mean actin gliding velocity of 19 individual M. soleus fibers as a function of the ELC MLC1sa/MLC1sb/v ratio. A decrease of actin gliding velocity with increasing MLC1sa/MLC1sb/v ratio is reflected by a linear regression to the velocity data with a slope of −0.0383 ± 0.007 (black line). Inset: On a BSA-coated assay chamber surface myosin extracted from individual type-I M. soleus fibers with a lower MLC1sa/MLC1sb ratio (<40% MLC1sa) moved actin filaments with 0.387 µm/s (±0. 014 µm/s SE, n = 3 muscle fibers representing light grey squares in large plot). Actin gliding on myosin prepared from M. soleus fibers containing >60% MLC1sa was significantly slower (0.314 ± 0.008 µm/s SE, n = 7 representing black squares in large plot, T = 23°C). Data points represent mean gliding velocities of individual muscle fibers, while bars represent mean values ± SE. Source data are available for this figure: SourceData F5.

MLC composition and actin filament gliding velocity of myosin extracted from individual type-I M. soleus fibers. (A) Example of MLC SDS-PAGE analysis of individual type-I M. soleus fibers. For each fiber, the respective relative content of MLC1sa (upper band) versus MLC1sb/v (lower band) was determined by densitometric analysis of the SyproRuby-stained 15% SDS-PAGE gel. Note that all tested M. soleus fibers contained both ELC isoforms; the majority showed a higher content of MLC1sa, which was not detected in the control ventricular myosin. (B) Mean actin gliding velocity of 19 individual M. soleus fibers as a function of the ELC MLC1sa/MLC1sb/v ratio. A decrease of actin gliding velocity with increasing MLC1sa/MLC1sb/v ratio is reflected by a linear regression to the velocity data with a slope of −0.0383 ± 0.007 (black line). Inset: On a BSA-coated assay chamber surface myosin extracted from individual type-I M. soleus fibers with a lower MLC1sa/MLC1sb ratio (<40% MLC1sa) moved actin filaments with 0.387 µm/s (±0. 014 µm/s SE, n = 3 muscle fibers representing light grey squares in large plot). Actin gliding on myosin prepared from M. soleus fibers containing >60% MLC1sa was significantly slower (0.314 ± 0.008 µm/s SE, n = 7 representing black squares in large plot, T = 23°C). Data points represent mean gliding velocities of individual muscle fibers, while bars represent mean values ± SE. Source data are available for this figure: SourceData F5.

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