PHYSIOLOGICALLY ACTIVE COMPOUNDS 255 



A very characteristic feature of denaturation is the dis- 

 appearance of the biological properties of the native protein. 

 On denaturation the physiological activities of hormones are 

 destroyed, enzymes lose their catalytic powers and the sero- 

 logical specificity of proteins disappears. The inactivation of 

 enzymes, in particular, seems to be one of the commonest 

 phenomena in laboratory practice and examples in the 

 scientific literature of thermostability among enzymes (e.g. 

 ribonuclease or lysozyme) or of their regeneration after 

 denaturation seem to be the exception rather than the rule.^"' 



The same may be said of serological specificity. For in- 

 stance, it is widely known that denatured egg albumin, like 

 other proteins, does not react nearly so well with the antibody 

 which is formed by the native protein."^ J. O. Erickson and 

 H. Neurath, however, believe that serological activity is asso- 

 ciated with structures which are the last to be affected by 

 denaturation."^ 



From all that has been said it follows that the biological 

 specificity of proteins and, in particular, the catalytic activity 

 of enzymes is related not only to a particular sequence of 

 amino acid residues in the polypeptide chains but also to 

 the way in which these chains are arranged inside the mole- 

 cule of any given protein. Owing to its extreme significance, 

 the structure of the protein molecule has long engaged the 

 attention of scientists. Many of them have tried to construct 

 a schematic representation of this structure on purely theore- 

 tical foundations. For example, D. M. Wrinch"* once did so, 

 mainly on the basis of geometrical considerations. 



A very interesting hypothesis concerning the structure of 

 the molecules of globular proteins has been formulated by 

 D. L. Talmud and S. E. Bresler."^ These authors assumed 

 that, as the result of the definite and regular sequence of 

 amino acid radicals, the non-polar (non-ionising) groups such 

 as the hydrocarbon radicals of alanine, leucine, ?5oleucine, 

 valine, phenylalanine, etc., were mainly arranged on one 

 side of the peptide chain, while the polar (ionising) groups 

 such as the radicals of aspartic and glutamic acids, serine, 

 arginine, lysine and histidine were arranged on the other. 

 This may be represented for the ideal case by the following 

 diagram (Fig. 17). 



