Rotational dynamics of spin-labeled F-actin during activation of myosin S1 ATPase using caged ATP

E. M. Ostap, David D Thomas

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The most probable source of force generation in muscle fibers in the rotation of the myosin head when bound to actin. This laboratory has demonstrated that ATP induces microsecond rotational motions of spin-labeled myosin heads bound to actin (Berger, C. L. E. C. Svensson, and D. D. Thomas. 1989. Proc. Natl. Acad. Sci. USA. 86:8753–8757). Our goal is to determine whether the observed ATP-induced rotational motions of actin-bound heads are accompanied by changes in actin rotational motions. We have used saturation transfer electron paramagnetic resonance (ST-EPR) and laser-induced photolysis of caged ATP to monitor changes in the microsecond rotational dynamics of spin-labeled F-actin in the presence of myosin subfragment-1 (S1). A maleimide spin label was attached selectively to cys-374 on actin. In the absence of ATP (with or without caged ATP), the ST-EPR spectrum (corresponding to an effective rotational time of approximately 150 microseconds) was essentially the same as observed for the same spin label bound to cys-707 (SH1) on S1, indicating that S1 is rigidly bound to actin in rigor.(ABSTRACT TRUNCATED AT 250 WORDS)

Original languageEnglish (US)
Pages (from-to)1235-1241
Number of pages7
JournalBiophysical journal
Issue number6
StatePublished - 1991

Bibliographical note

Funding Information:
This work was supported by grants to Dr. Thomas from the National Institutes of Health (NIH) (AR 39754) and the Minnesota Supercom-

Funding Information:
puter Institute. Mr. Ostap was supported by a Biophysics Training grant from NIH (GM 08277-03).


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