A THEORY OF THE PRIMARY EVENT IN MUSCLE 



ACTION 



MANUEL F. MORALES and JEAN BOTTS, Division of Physical 

 Biochemistry, U. S. Naval Aiedical Research Institute, Bethesda, Maryland 



The fundamental problem in muscle physiology is not hard 

 to describe : Somewhere in the multitude of reactions going on 

 in the excited fiber there must be a "chemical" reaction which 

 proceeds in such a way that it requires, compels, or achieves an 

 extensive condensation of matter along one axis of space. The 

 problem is to identify the participants of the "reaction" and the 

 matter condensed in this transduction between "chemical" and 

 mechanical energy. 



At the time of this writing, knowledge is sufficiently ad- 

 vanced to warrant reasonable speculation about the nature of 

 this primary event, but not so advanced as to discriminate with 

 assurance between two or three hypotheses. For example, it 

 has been shown that two rather pure proteins extractable from 

 muscle, viz., myosin and actin, have an attraction for one another 

 which can be largely abolished by the nucleotide, adenosinetri- 

 phosphate (ATP). It is a priori reasonable to think that in 

 muscles myosin and actin are so disposed that the attraction be- 

 tween them causes elements of the two proteins to condense 

 axially whenever ATP is withdrawn from the system, and to 

 separate passively whenever ATP is introduced into the system. 



609 



