do this. There are still possibilities for bringing this structure into 

 line with our earlier concepts. One could suppose, e.g., the ATP 

 to produce some local change on the H which would make the 

 L's fold back on it, producing thus a shortening, or contraction. So 

 there are ways out, though not nice or good ones. 



If a theory is good, then any newer knowledge should support 

 it and contribute to clarification, as was the case with intermediary 

 metabolism. With myosin things are going the other way. Andrew 

 Szent-Gyorgyi and Borbiro showed that the meromyosins also are 

 built of subunits, protomyosins. The protomyosins are of equal 

 size and rather small. Their MW is about 4500 g, which means 

 that one meromyosin is built of a greater number of them, the L 

 of about 20, the H of about 50. These protomyosins are held to- 

 gether by secondar)' forces only, such as H-bonds, and van der 

 Waal's and electrostatic attractions. If we call a molecule a struc- 

 ture of atoms held together by covalent bonds, then the myosin 

 particle is no molecule at all, only an aggregate. The structure is 

 symbolized in a very crude way in Fig. 2a. It is difficult to see how 

 such a structure could fold; it seems more likely that contraction is 

 not a folding at all, but a rearrangement of protomyosins within 

 the particle, which rearrangement leads to a more rounded, short- 

 ened form, as symbolized in Fig. 2b. In order to produce such a 

 rearrangement, many weak forces must be disturbed which keep 

 the protomyosins together. It is impossible to see how a bond en- 

 ergy, enclosed in a ^P, could cause such a disturbance, especially 

 if that ^P is far away, on the H-meromyosin. 



We can thus sum up the situation by saying that we do not 

 know how muscle contracts, how it uses bond energy to produce 

 work, and the more we know about its structure the less we under- 

 stand its function. We might have arrived here at the edge of the 

 chasm which seems to extend through medicine and biology and 

 may be responsible for its "chiaroscuro." 



