Binding of myosin subfragment-1 to F-actin.
During a part of the hydrolytic cycle, myosin head (S1) carries no nucleotide and binds strongly to an actin filament forming a rigor bond. At saturating concentration of S1 in rigor, S1 is well known to form 1:1 complex with actin. However, we have provided evidence that under certain conditions S1 could also form a complex with 2 actin monomers in a filament (Andreev, O.A. & Borejdo, J. (1991) Biochem. Biophys. Res. Comm. 177, 350-356). This view was recently challenged by Carlier & Didry (Carlier, M-F. & Didry, D. (1992) Biochem. Biophys. Res. Comm. 183, 970-974) who interpreted our data by suggesting that F-actin underwent a simple depolymerization and implied that, when only actin in the F-form was scored, the real stoichiometry in our experiments was 1:1. We show here that under conditions of our experiments less than 8% of actin was depolymerized. Moreover, we have repeated the experiments in the presence of phalloidin and show that under these conditions too, when S1 was added slowly to a fixed concentration of F-actin, it formed a different complex with F-actin than when it was added quickly. This confirms our original conclusion that S1 can bind actin in two different ways and shows that depolymerization of F-actin is not responsible for this finding.
Andreev
O
O
Baylor Research Institute, Baylor University Medical Center, Dallas, TX 75226.
Borejdo
J
J
D000199:Actins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D002850:Chromatography, Gel; D007700:Kinetics; D008027:Light; D009132:Muscles / Q000378:metabolism; D015879:Myosin Subfragments / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D009391:Nephelometry and Turbidimetry; D011485:Protein Binding; D011817:Rabbits; D012542:Scattering, Radiation; D014461:Ultracentrifugation
D000199:Actins; D015879:Myosin Subfragments