IMOLECULAR STRUCTURE IN PROTOPLASM 



179 



seem to be in agreement with the varj^ing 

 water relations of gelatin as shown by 

 X-ray diffraction patterns. In Table VIII 

 the increase in side-chain spacing may be 

 noted where increase in the amonnt of 



to determine with a very great degree of 

 assnrance the existence of the long, ex- 

 tended chain in fluids, although in some 

 solid forms the X-ray work seems to point 

 conclusively to their existence. 



TABLE VIII 



Intermolecular Spacixgs of Gelatin and Water Mixti:res from X-ray Diffraction Studiesi 



1 This tal:>le is modified from data given by Herrmann, Gcrngross and Abitz (1930). 



water present is accompanied by an in- 

 crease in spacing from 10.4 A up to 17 A ; 

 while the back-bone spacing remains un- 

 changed at 4.4 A until a sufficient amount 

 of water is present; then at 33 per cent 

 water the chains become separated to about 

 7.0 A, and the interleaved water molecules 

 bring about the half spacing of about 

 3.5 A. These alternating back-bone and 

 water layers apparently remain intact even 

 when 90 per cent water is present; while 

 the side-chain spacings become too irregu- 

 lar at about 75 per cent water to be recog- 

 nizable in the X-ray photograph. These 

 changes for the first three columns of Table 

 VIII, where the water content is given as 

 0.2 per cent, 15 per cent, and 33 per cent, 

 are illustrated by the diagrams in Fig. 7. 

 If the diagrams were given for the remain- 

 ing columns which have higher water con- 

 tent, the spacings for the side chains only 

 would show increase. 



Practically every investigator interested 

 in proteins, where the physical structure is 

 involved, has found evidence of particles 

 of sizes var^'ing from those with a molecu- 

 lar weight of about 9,000 up to many with 

 about 35,000 and 70,000, and a few even 

 up into the millions (Svedberg 1937 ; 1939). 

 They also vary in shape from globular to 

 much elongated forms (Neurath 1938). Up 

 to the present time it has not been possible 



It seems reasonable, then, to assume that 

 in the construction of protein particles 

 chains of unknown length exist, either as 

 long chains folded back and forth or as 

 short lengths. In the cytoplasm these are 

 probably hydrated, at least to the extent of 

 satisfying the available component hydro- 

 philic groups; that is, the atomic groups 

 in which oxygens and nitrogens are pres- 

 ent. The amount of hydration most likely 

 to occur in these protein particles on this 

 assumption is about 35 to 40 per cent 

 water. Particles in the cytoplasm are 

 known to have a specific gravity of about 

 1.15, which is equivalent to a water-protein 

 mixture of 40 to 50 per cent water (Heil- 

 brunn 1928 ; Bechhold and Schlesinger 

 1931, 1933; Schlesinger 1932, 1934). Thus 

 our theoretical hydrated particle of 35 to 

 40 per cent corresponds fairly well in water 

 content with that of the cytoplasmic par- 

 ticle, and since the latter is known to be 

 mostly protein which, when dried, shows 

 the existence of the chain spacings, 4.5 A 

 and 10.5 A, it seems reasonable to make use 

 of this layered protein-chain particle as a 

 working conception for protoplasmic parti- 

 cles in general. 



On this assumption the particles consist 

 of layers of chains. In one direction the 

 layers are spaced quite consistently about 

 7 A apart, where this is the back-bone dis- 



