Peptides corresponding to the N-terminus of skeletal myosin light chain 1 (rsMLC1 1–37) and the short loop of human cardiacb-myosin (hcM398–414) have been shown to interact with skeletal F-actin by NMR and fluorescence measurements. Skeletal tropomyosin strengthens the binding of the myosin peptides to actin but does not interact with the peptides. The binding of peptides cor-responding to the inhibitory region of cardiac troponin I (. hcTnI128–153) to F-actin to form a 1 : 1 molar complex is also strengthened in the presence of tropomyo-sin. .