36 



The Structure of Protoplasm 



bone as Astbury had originally postulated, but the true state of 

 affairs is probably somewhat like that shown in Figure 4. 



Myosin and the protein isolated by Mirsky appear to have some 

 characteristics of both groups. They are much more elongated than 

 the corpuscular proteins, yet are soluble in water. Both show double 



OC 



f 



collagen 



supercontracted 



Fig. 4. Possible folded states of the back-bone in fibrous proteins. (After 

 Astbury.) 



refraction of flow. Both are exceedingly sensitive to the effects 

 of denaturing agents. Even salts, such as CaCL or LiCl, at low con- 

 centrations rapidly destroy the streaming double refraction of 

 myosin (9) . 



Astbury (3) has presented evidence to show that myosin in 

 relaxed muscle is in the a state; on muscular contraction, he claims 

 it becomes "supercontracted." It is certain, in any case, that the 

 insolubility accompanying muscular contraction is not identical 

 with the denaturation of a corpuscular protein, for no alteration in 

 the number of sulfhydryl groups takes place (25) . On treating myo- 



