'^\OAl 



1. The Problem Is Stated 



The problem is: how does energy drive life? How does it move 

 the living machine? This is one of the most basic problems of 

 biology and, at present, there is no answer to it. So it is possible 

 that the "oscuro," alluded to in the Introduction, is due to our in- 

 ability to answer this question. 



In order to avoid losing ourselves in generalities, we have to 

 take a specific example. I will take a little experiment I made a 

 few years ago. In this experiment I took a strip of muscle (I chose 

 the musculus psoas of the rabbit), put it into clUuted glycerol, and 

 kept it in the glycerol for a few days in the refrigerator and for a 

 few weeks in the deep freeze. Then I suspended it in 0.1 Al KG 

 at room temperature, added a little Mg, and added ATP in the 

 same concentration as the muscle contained it in vivo. The muscle 

 contracted and developed the same tension as it developed maxi- 

 mally in the living animal. If we identify life with motion we 

 could say: the muscle came to life again. In this process the ATP 

 was split, losing its terminal phosphate which was linked to it by 

 a P — O — P. Since we know that this link is a so-called high-energy 

 phosphate bond, -^P, and no other energy donor was present, it 

 is evident that the energy which moved the muscle was the energ)' 

 of this '^P, and so we can narrow our problem down and ask how 

 did the energy of the '^P move the muscle? 



Progress in the chemistry of muscle made it possible to simplify 

 tl^ie problem even further. I showed almost two decades ago that 

 contraction in muscle is, essentially, the interaction of actomyosin 

 (a complex formed of two proteins, actin and myosin) with ATP 

 and ions. Of the two proteins, myosin is responsible for the ele- 

 mentary act of contraction and so we can simplify our proposition 



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