Fig. 8.

Mechanism for converter 11e’s different influence on indirect flight muscle (IFM) contraction speed compared with jump muscle shortening velocity. A: IFM frequency at which maximum power was generated (f_max) vs. jump muscle maximum shortening velocity (v₀; r² = 0.98 and P = 0.008, excluding 11e). B: IFM f_max vs. jump muscle optimal velocity for power production (V_opt; r² = 0.97 and P = 0.005, excluding 11e). C: interaction of the exon 11e converter (blue) and the ELC (yellow, variable domain in orange). The IFM isoform of the ELC is shown, with Q153 and E83 of the ELC interacting strongly with Q732 of the 11e converter. D: the non-IFM isoform of the ELC (found in the TDT and other muscles) is shown, with V153 and E83 interacting weakly with Q732 of the 11e converter. The difference in isoform-dependent interaction strength provides a possible explanation for 11e’s imparting fast muscle kinetics (e.g., v_opt and v₀) in the TDT and slow muscle kinetics in the IFM (e.g., f_max). The other 4 versions of the converter have amino acids at this position (732) that do not result in as big of a change in interaction strength when expressed in conjunction with the different essential light chain (ELC) isoforms.