Proteins and Protoplasmic Structure 37 



sin with acid or heat, the SH groups aUer in number (25), and 

 Astbury believes the extended j3 form is then produced. If so, it is 

 strange that the effect of these agents is to remove the streaming 

 double refraction (9) . 



Likewise, when the sea urchin egg was fertilized, Mirsky found 

 no change in SH groups accompanying the decrease in protein solu- 

 bility (24) . These groups appeared, however, if the egg was treated 

 with acid. Of all the ways of coagulating myosin in vitro, Mirsky 

 finds that only dehydration produces no change in SH groups. Dehy- 

 dration readily renders the isolated egg protein insoluble. He sug- 

 gests, therefore, that both muscular contraction and fertilization act 

 as dehydrating agents which permit the protein molecules to come 

 close enough together to combine with each other and become insol- 

 uble without much intramolecular disturbance. 



Banga and Szent-Gyorgyi (4) have recently proposed that, 



"Whenever nature needs a mobile protein (serum albumin and globu- 

 lin, secretions like milk-proteins, hormones like insulin, different 

 enzymes, etc.) it applies the globular shape, and whenever it wants to 

 build a solid structure it applies the rod shape. Proteins have been found 

 to be mostly globular because unconsciously the rnobile and more 

 easily accessible proteins have been selected for study." 



These authors have succeeded in dispersing some of the struc- 

 tural proteins from tissues like kidney and from chloroplasts and 

 find the extracts to be highly viscous and thixotropic and to exhibit 

 streaming double refraction. They believe this last property indi- 

 cates that these structural proteins belong to the fibrous group. 

 Banga and Szent-Gyorgyi used salt solutions containing 30 per cent 

 urea to disperse these proteins, a substance capable of inducing 

 marked changes in the structure of other proteins. Whether or not 

 these dispersed tissue proteins have the same constitution as the 

 native forms is questionable. They seem to be different from the 

 corpuscular proteins, for these do not exhibit streaming double re- 

 fraction after treatment with the salt-urea solution. This work is 

 an interesting beginning in a difficult, but important, field. 



It is obvious that myosin and Mirsky's egg proteins are very 

 different in their properties from the corpuscular proteins. The 

 evidence indicates, furthermore, that they exhibit important differ- 

 ences from the truly fibrous proteins, in spite of the findngs of Banga 

 and Szent-Gyorgyi. Unlike the fibers, these intraprotoplasmic pro- 

 teins are characterized by an extreme sensitivity to heat or to elec- 

 trolytes. It is possible that they are extended to a fibrous condition 



