© 2006 The Japanese Biochemical Society.
Regular Paper |
Protein Osmotic Pressure and Cross-Bridge Attachment Determine the Stiffness of Thin Filaments in Muscle Ex Vivo
Dipartimento di Biochimica e Biologia Molecolare, Univerità di Ferrara, Via Borsari 46, 44100 Ferrara, Italy
* To whom correspondence should be addressed. Phone: +39 0532 291421, Fax: +39 0532 202723, E-mail: gre{at}dns.unife.it
The properties of some models of the actin filament are compared with those of the thin filament in muscle. The greater stiffness of thin filaments ex vivo with respect to F-actin in vitro is attributed to the effect of both protein osmotic pressure and the attached cross-bridges. By comparing the stiffness of thin filaments in vitro and in isometric and rigor muscles the stiffness of thin filaments in relaxed muscle is computed. The upper limit of thin filament stretching is deduced to approach 
10 nm µm–1. It is also calculated that, on stretching by 2.02 nm of the fully non-overlapped thin filament or by 1.59 nm of the thin filament on isometric contraction, the energy released on the hydrolysis of one molecule of ATP is fully used up.