by considering myosin instead of muscle, and ask how the energy 

 of ^P moves myosin? 



We know from the studies of Edsall and Weber that the myo- 

 sin molecule is a thin filament. So without knowing any more de- 

 tails about it, we can form two different pictures of the process in 

 which the energy of the '^P is transferred to this filament and 

 produces contraction. The one would be to suppose that the mole- 

 cule carrying this ^P, in our case ATP, enters into some chemical 

 reaction with the myosin, as the result of which a local change is 

 produced in the protein which leads to its folding. An ATP- 

 myosin complex would have to be formed which then splits up, 

 leaving behind phosphate, ADP, and the altered myosin. Such a 

 reaction finds many analogies in the "group transfer reactions" of 

 the intermediary metabolism and, in principle, could be described 

 with symbols of classical chemistry. 



The alternative picture is based on the supposition that the ATP 

 molecule does not enter into any such local reaction, but the bond 

 energy of its ^P's becomes released in a more active and mobile 

 form which then is transferred to the myosin molecule, moves 

 through it, and produces in its vv'ake changes which, somehow, 

 lead to contraction and could adequately be described only in terms 

 of quantum mechanics. Compared to the first, this picture is vague, 

 has no analogies in intermediary metabolism, and one may ask 

 why make such hazy pictures if we can make clear ones with deep 

 roots in existing knowledge? 



The inadequacy of the earlier classical pictures was brought out 

 by the advances made in the chemistry of myosin. The more we 

 learn about myosin the less we understand it, which suggests that 

 we are looking at it in the wrong way. Continuing some studies 

 made by Gergely, Perry, and Mihalyi, Andrew Szent-Gyorgyi 

 showed the myosin molecule to be built of two kinds of subunits, 

 "meromyosins" which, within the molecule, stand in a row in 

 series (Lauffer and Andrew Szent-Gyorgyi ) . If Laki and Caroll's 

 value of the molecular weight of myosin is correct, one molecule of 



