Biophysical Journal, February 2000, p. 927-939,
Vol. 78, No. 2
The Effect of Polyethylene Glycol on the
Mechanics and ATPase Activity of Active Muscle Fibers
Marc K. Chinn,* Kathryn
H. Myburgh, Truc Pham,* Kathleen Franks-Skiba,* and
Roger Cooke*
*Department of Biochemistry and
Biophysics, Cardiovascular Research Institute, University of California, San
Francisco, California 94143 USA, and Department of Physiology, University of
Stellenbosch, Stellenbosch 7600, South Africa
We have used polyethylene glycol (PEG) to
perturb the actomyosin interaction in active skinned muscle fibers. PEG is known
to potentiate protein-protein interactions, including the binding
of myosin to actin. The addition of 5% w/v PEG (MW 300 or 4000)
to active fibers increased fiber tension and decreased shortening
velocity and ATPase activity, all by 25-40%. Variation in [ADP] or
[ATP] showed that the addition of PEG had little effect on the
dissociation of the cross-bridge at the end of the power stroke.
Myosin complexed with ADP and the phosphate analog Vi or AlF4
binds weakly to actin and is an analog of a pre-power-stroke state.
PEG substantially enhances binding of these states both in active
fibers and in solution. Titration of force with increasing [Pi]
showed that PEG increased the free energy available to drive the
power stroke by about the same amount as it increased the free
energy available from the formation of the actomyosin bond. Thus PEG
potentiates the binding of myosin to actin in active fibers, and it
provides a method for enhancing populations of some states for
structural or mechanical studies, particularly those of the normally
weakly bound transient states that precede the power stroke.
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