Figure 2.

Increasing KCl and ADP concentrations progressively decrease the myosin SRX population, particularly in BcSTFs.A, the effect of KCl on the myosin SRX population in various myosin models. Symbols represent the experimental data, and the corresponding best fits serve as a guide to the eye (linear for BcS1 and BcHMM but exponential for BcSTFs). Data are normalized to the myosin SRX values at 5-mM (0.005 M) KCl concentration in respective systems. B, the concentration-dependent effect of ADP on myosin SRX population in BcSTFs, BcHMM, and BcS1. In these experiments, care was taken to keep the total nucleotide (ATP + ADP) concentration to 2 mM in each case. Data are normalized to the myosin SRX values at the 0-mM ADP (2-mM ATP) in respective systems. The dependency of myosin SRX population on the ADP concentration was fitted to a linear regression model, and the resulting slopes were compared among groups. Symbols represent the experimental data, and the corresponding best fits (linear) serve as a guide to the eye. BcS1 refers to bovine cardiac myosin subfragment-1, BcHMM refers to bovine cardiac heavy meromyosin, and BcSTFs refers to bovine cardiac synthetic thick filaments. Data are expressed as the mean ± SEM (n ≥ 8 from at least two experiments). SRX, super-relaxed.