The Journal of General Physiology, Vol 69, 37-55, Copyright © 1977 by The Rockefeller University Press
Tension generation by threads of contractile proteins
R Crooks and R Cooke
Threads of contractile proteins were formed via extrusion and their
isometric tensions and isotonic contraction velocities were measured. We
obtained reproducible data by using a new and sensitive tensiometer. The
force-velocity curves of actomyosin threads were similar to those of
muscle, with isometric tensions of the order of 10g/cm2 and maximum
contraction velocites of the order of 10(-2) lengths/s. The data could be
fitted by Hill's equation. Addition of tropomyosin and troponin to the
threads increased isometric tension and maximum contraction velocity.
Threads which contained troponin and tropomyosin required Ca++ for
contraction and the dependence of their isometric tension on the level of
free Ca++ was like that of muscle. The dependence of tension or of
contraction velocity upon temperature or upon ionic strength is similar for
actomyosin threads and muscle fibers. In contrast, the dependence of most
parameters which are characteristic of the actomyosin interaction in
solution (or suspension) upon these variables is not similar to the
dependence of the muscle fiber parameters. The conclusion we have drawn
from these results is that the mechanism of tension generation in the
threads is similar to the mechanism that exists in muscle. Because the
protein composition of the thread system can be manipulated readily and
because the tensions and velocities of the threads can be related directly
to the physiological parameters of muscle fibers, the threads provide a
powerful method for studying contractile proteins.
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