Orientation and Mobility of Actin in Different Intermediate States of the ATP Hydrolysis Cycle

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S. S. Khaimina¹, A. Wrzosek², R. Dabrowska², and Yu. S. Borovikov^1*

¹Institute of Cytology, Russian Academy of Sciences, Tikhoretsky pr. 4, 194064 St. Petersburg, Russia; fax: (7-812) 247-0341; E-mail: boroviko@mail.cytspb.rssi.ru

²Nencki Institute of Experimental Biology, Polish Academy of Sciences, 02093 Warsaw, Poland

^* To whom correspondence should be addressed.

Received May 17, 2004; Revision received July 13, 2004

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Using polarization fluorimetry, we have investigated conformational changes of FITC-phalloidin-labeled F-actin in ghost muscle fibers. These changes were induced by myosin subfragment-1 (S1) in the absence and presence of MgADP, MgAMP-PNP, MgATPgammaS, or MgATP. Modeling of various intermediate states was accompanied by discrete changes in actomyosin orientation and mobility of fluorescent dye dipoles. This suggests multistep changes of orientation and mobility of actin monomers during the ATPase cycle. The most pronounced differences in orientation (~4°) and in mobility (~43%) of actin were found between the actomyosin states induced by MgADP and MgATP.

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KEY WORDS: muscle contraction, ATP analogs, intermediate states of actomyosin, conformational changes of actin, fluorescence polarization

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