EFFECT OF HYPOTHYREOSIS ON ACTIN SUBDOMAIN-1 MOVEMENT INDUCED BY MYOSIN SUBFRAGMENT 1-BINDING IN FAST AND SLOW RAT SKELETAL
MUSCLES
V. P. Kirillina,1,* A. Jakubiec-Puka,2 Yu. S. Borovikov 1
1 Institute of Cytology RAS, St. Petersburg, Russia,
and 2 Nencki Institute of Experimental Biology, Polish Academy of Science, Warsaw, Poland;
* e-mail: kirill@mail.cytspb.rssi.ru
Orientation and mobility of fluorescent probe N-((iodoacetyl)-(1-naphtyl-5-sulpho-ethylenediamine)(
1.5-IAEDANS)) specifically bound to Cys-374 of actin in ghost muscle fibers isolated from fast and slow
rat muscles were studied by polarized fluorimetry in the absence and presence of myosin subfragment-1 (S1) in
intact rats and in the animals with gradual (during 2—5 weeks) reduction of thyroid hormones synthesis (hypothyreosis
development). S1 binding to F-actin of ghost muscle fibers was shown to induce changes in orientation
of the dipoles of the fluorescent probe 1.5-IAEDANS and in the relative amount of the randomly oriented fluorophores
that indicated changes in actin subdomain-1 orientation and mobility resulting from the formation of
its strong binding with S1. This effect is markedly inhibited by hypothyreosis development. The maximal effect
of hypothyreosis is observed after 34 days of disease development. It is suggested that the change of thyroid status
in the muscle inhibits the ability of F-actin to form strong binding with myosin which is essential for force
generation.
Key words: muscle contraction, hypothyreosis, actin conformational changes, F-actin, polarized fluorescence
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