Kinetics of binding of caldesmon to actin.
The time course of interaction of caldesmon with actin may be monitored by fluorescence changes that occur upon the binding of 12-(N-methyl-N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl))-labeled caldesmon to actin or to acrylodan actin. The concentration dependence of the observed rate of caldesmon-actin binding was analyzed to a first approximation as a single-step reaction using a Monte Carlo simulation. The derived association and dissociation rates were 10(7) M-1 s-1 and 18.2 s-1, respectively. Smooth muscle tropomyosin enhances the binding of caldesmon to actin, and this was found to be due to a reduction in the rate of dissociation to 6.3 s-1. There is no evidence from this study for a different mechanism of binding in the presence of tropomyosin. The fluorescence changes that occurred with the binding of 12-(N-methyl-N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl))-labeled caldesmon to actin or actin-tropomyosin were reversed by the addition of myosin subfragment 1 as predicted by a competitive binding mechanism.
Chalovich
J M
JM
Department of Biochemistry, East Carolina University School of Medicine, Greenville, North Carolina 27858-4354, USA.
Chen
Y D
YD
Dudek
R
R
Luo
H
H
D000199:Actins / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D002148:Calmodulin-Binding Proteins / Q000378:metabolism*; D005456:Fluorescent Dyes; D007700:Kinetics; D008969:Molecular Sequence Data; D009130:Muscle, Smooth / Q000378:metabolism; D011485:Protein Binding; D014335:Tropomyosin / Q000378:metabolism; D014422:Turkeys
D000199:Actins; D002148:Calmodulin-Binding Proteins; D005456:Fluorescent Dyes; D014335:Tropomyosin