60 



Unlike covalent bonds, such links have no fixed valency angles. 

 This makes the whole structure comparable to a string of beads, 

 or a bundle of such strings, the most characteristic feature of which 

 is pliability, the lack of resistance to deformation. The forces be- 

 tween protomyosins can be expected not only to hold these parti- 

 cles together, but also to tend to pull them together from the 

 fibrous form into a more compact, rounded, and shortened shape 

 (Fig. 2). If, all the same, we find the myosin particles in solution 

 or in resting muscle stretched out to a straight filament there must 

 be forces which counteract the mutual attractions which tend to 

 shorten the particle. The problem of contraction is thus not what 

 makes the particles shorten but what keeps them extended when 

 at rest, or stretches them out again after contraction? 



It is suggested that what keeps the myosin particle extended, 

 counteracting the forces of contraction, are the expanding water 

 structures which the particles build around themselves, while con- 

 traction is due to the collapse of these water structures with the 

 consecutive rearrangement of protomyosins into a shortened aggre- 

 gate. The latter changes would have to be brought about by the 

 energy of ATP. In order to effect such a change the (£) of ATP 

 would have to be transformed into the more mobile £* which 

 can interact with the water structures. 



The theory proposed is, in its simplest form, the following: the 

 myosin particle is kept stretched out by its water structures. Con- 

 traction is induced by the collapse of these structures, the reestab- 

 lishment of which is relaxation.^ The question is how far is this 

 theory in agreement with known facts about muscle or to what 

 extent can it explain them.'' 



Myosin, in a watery solution, has a high viscosity. This indicates 



^ The fibrous molecules of deoxyribose nucleic acid, dissolved in water, 

 are known to shorten by 30% or so on addition of salts, Jacobson found 

 under these conditions (using NaCl) that the water structure collapsed. 

 Possibly, the collapse of these structures is responsible for the shortening, 

 making the process analogous to muscle contraction, as supposed by the 

 theory presented here. 



