PHYSIOLOGICALLY ACTIVE COMPOUNDS 



2r. 



0/ 



If this were to happen, additional Knkages would arise 

 between adjacent turns of the spiral, in particular hydrogen 

 bonds between the — nh — and -co — groups. The elucida- 

 tion of the actual arrangement of the amino acid residues 

 in the polypeptide chains of such a typical globular protein 

 as insulin seems to be does not, however, confirm this idea. 

 In this case there is an irregular sequence of polar and 

 non-polar residues (Fig. 19) so that the chain will not be 

 twisted up to form a globule in the way Talmud and Bresler 

 imagined."" 



O Q 



O 



O 



O 



006 



Fig. 19. Polypeptide chain B of the molecule of insulin. 



Direct investigation of the structure of corpuscular pro- 

 teins by the diffraction of X-rays"^ and infra-red rays"^ shows 

 that this structure is, in fact, far more complicated than any 

 of the schemes drawn up on the basis of general physico- 

 chemical considerations. 



In her review B. W. Low"^ points out that of the whole 

 number of proteins which have been studied in this respect 

 " at best a ' bird's-eye ', long distance view of some protein 

 molecules has been derived. It is, however, far from a 

 detailed or precise description of the molecular architec- 

 ture. . . ." 



Nevertheless, it may now be held to be established that 

 the essential molecule of corpuscular proteins does not consist 

 of globules but of bundles of polypeptide chains."^ A struc- 

 ture of this sort may be made up either of chains which 

 are, in fact, separate (as has been shown in the case of insulin) 

 or of parts of a single polypeptide chain pleated like a ribbon 

 folded back and forth on itself. 



In a molecule of native corpuscular protein these chains 

 are twisted or folded in a definite way or curled into helices. 

 It is very likely that in some, though not in all, corpuscular 



17 



