252 ORIGIN OF STRUCTURES AND FUNCTIONS 



Unfortunately we have, at present, only a very limited 

 amount of information on this subject and what we have is 

 concerned mainly with enzymes of low molecular weight. 

 In particular, C. Fromageot and his colleagues^^ and later 

 K. Ohno'* have established the sequence of the amino acids 

 in some separate fragments of lysozyme (molecular weight 

 14,700). A. Thompson*^ obtained from lysozyme a series of 

 penta-, tetra-, tri- and dipeptides and worked out the order 

 in which the amino acids are arranged in them. This order 

 has not, however, been established for lysozyme as a whole. 

 Similar studies with ribonuclease (molecular weight 15,000) 

 are on the way to giving a complete picture of the sequence 

 of amino acids in it.^° 



On the basis of what we know we can already put forward 

 the hypothesis that the sequence of the amino acid residues 

 in the polypeptide chains of various enzymes is not less com- 

 plicated than that in insulin and other similar hormones 

 and also that, like the biological activity of the hormones, 

 that of the enzymes is determined, in the first place, by this 

 specific structure of the polypeptide chains. 



It must not be forgotten that in the protein molecule these 

 chains are disposed in a definite three-dimensional arrange- 

 ment, the structure of which is of extreme importance in 

 determining the biological characteristics of the protein in 

 question. The chemical potentialities of the side chains and 

 of the polar terminal groups of the amino acid residues are 

 not only realised in external reactions but also in forming 

 internal linkages. This leads to an orderly twisting of the 

 peptide chain and its unification into an extremely well-knit 

 three-dimensional structure with an ordered internal con- 

 figuration. 



A structure of this sort is very characteristic of the protein 

 molecule. Other filamentous molecules, such as rubber, can 

 also curl up into lumps as a result of the thermal motion of 

 their different parts. However, the structure of these lumps 

 seems to be fortuitous. The separate parts are not connected 

 together in any orderly way and the lump may easily be 

 uncurled merely by the application of mechanical tension. 



The internal structure of the protein molecules, on the 

 other hand, seems to be perfectly orderly. In them the separ- 



