Peptide competition of actin activation of myosin‐subfragment 1 ATPase by an amino terminal actin fragment

Abstract
The amino‐terminal region of actin participates in the binding of myosin subfragment 1 (S1) during cross‐bridge cycling, thereby assisting in the activation of the magnesium‐dependent myosin ATPase. Effects of three actin fragments on the magnesium‐dependent S1 and acto‐S1 ATPase activities in solution were studied. One of the peptides, containing residues actin 1–44, mimicked the S1 ATPase‐activating properties of actin and in turn inhibited acto‐S1 ATPase both in a concentration‐dependent manner. This suggests peptide competition for the actin binding site on myosin. The other fragments, residues actin 1–18 and 82–119, respectively, had no detectable effect on S1‐ and acto‐S1 ATPase activity.