2 PROTEINS 359 



triphosphatase is intimately tied to myosin or may even be a part of 

 this protein molecule (Needham, 1942 a, b; Potter, 1944). The 

 intimate interrelation of the mechanics of the contractile muscle with 

 chemical reactions is shown by Hill (1950). 



We have first to discuss the morphological side of the problem. 

 When muscle contracts, the polypeptide chains coil up. Both extended 

 and relaxed muscle have the a-keratin structure, which becomes dis- 

 orientated on contraction (Huxley and Perutz, 195 i). Actually the 

 same thing occurs as in the supercontraction of the keratin chains, 

 with the difference, of course, that in the case of muscle the phe- 

 nomenon is reversible and can be voluntarily induced. A relaxed 

 muscle frozen in liquid air splits up into fibres, whereas a contracted 

 muscle disintegrates into small lumps (Meyer and Mark, 1950). 

 Furthermore, contraction wipes out the X-ray diagram. Roughly 

 speaking, a contracted muscle is amorphous like unextended 

 rubber, whereas in the relaxed state it is crystalline like elongated 

 rubber. 



Notwithstanding the enormous mass of literature on the physio- 

 logical processes involved in muscular contraction (Verzar, 1945; 



Faure-Fremiet, 1946), we do not yet 

 (^-co^ know what special process it is that 



Hydration- Induccs the folded polypeptide chains 



to supercontract. K. H. Meyer (1929) 

 ^fooj \<:Zi:>NH^ suggests that fundamentally it is the 



_,^„ ><CZII>coo" mutual repulsion of groups bearing the 



— ^ ^^^^coo~ same charge, e.g.,-COO~groups, which 



M~ -^ V. prevents the chains in the relaxed muscle 



Ph^^ ^"^'^^ ^ from crumpling. This occurs when the 



Fig. 178. Contraction of the poly- chain is in repose at a Ph of 7.4, viz., in 



peptide chains in the isoelectric ^^ ^[y^^Unc medium (see Fig. I78). Now 



state (I.E. P.) (after K. H. Meyer, ^ , 



ic,2c,), if by some physiological process the 



pjj of the muscle serum is reduced to 

 4.7, which corresponds to the isoelectric point of the protein actin, 

 the amino groups become positively charged and the groups with the 

 opposite electric charge are attracted to the point of contact and the 

 chains coil up. Kuhn and Hargitay (195 i) have calculated these 

 attractive and repulsive forces foi the case of polyacrylic acid, which 

 contracts in an acid and expands in an alkaline medium. They find 



