2 PROTEINS 3^9 



proximately to the globular molecules of the reserve proteins, but only 

 capable of existence in equilibrium with molecules of the solvent. 

 Where there is denaturation, these loosely-knit complexes would dis- 

 sociate and long chains would begin to form across the intervening 

 spaces. This would explain why denatured reserve proteins become 



NH. ,C0 



— -NH-CHR-COy^ iNH-CHR-CO-NH CO-NH-CHR-CO ^NH-CHR-CO- — 



CO-CHR-NH' *C0-CHR-NH-C0 NH-Cn-CHR-NH ,CO-CHR-NH— 



—NH-CHR-CO^ ,NH-CHR-CO-NH CO-NH-CHR-CO ^NH-CHR-CO— 



— NH-CHR-NH' ^CO-CHR-NH-CO NH-CO-CHR-NH. CO-CHR-NH— 



CO *NH 



Fig. 165. Molecular structure of a protein crystalloid. The arrows mark the bonds which, 



in "degeneration" to a fibre protein, are resolved to form bridges over the intermediate 



spaces (which contain solvent) to the neighbouring molecules, by which means straight 



chains come into existence (from Mark and Philipp, 1937). 



less digestible, since in this process the polypeptide compounds pass 

 from a loosened soluble form to the insoluble chain lattice form ,of 

 the frame-protein type (see Fig. 90, p. 136). 



Miss Wrinch (1937) suggests that ring formation of polypeptide 

 chains may be responsible for the globular shape of reserve protein 

 molecules. According to her "cyclol theory", the chains would form 

 hexagons by ring folding and forming a bridge bond at the open 

 position between the NH and CO groups. If, by tTiis scheme, six 

 amino acids are assigned to a cyclol six-ring, the result is three regular 

 hexagons arranged trigyrically around a central hexagon. This ternate 

 arrangement falls into line with the trigonal or hexagonal crystal 

 system of the crystallized reserve proteins. For each bridge formed, 

 an alcoholic C(OH) group comes into existence (see page 158), 

 all the hydroxyls of which lie on the same side of the ring system; 

 this will therefore have a hydrophilic and a hydrophobic side and 

 there will thus be a tendency towards double layer formation. On this 

 view, the protein crystalloids are to be conceived as packets of double 

 layers of this kind, the hydrophilic planes being responsible for the 

 ability of the crystal lattice to swell. 



In recent years, it has become doubtful whether in globular 

 proteins the peptide linkages characteristic of fibrillar proteins are 

 already preformed (Jordan, 1947; Scheibe, 1948). Because of their 



