100 UNITY AND DIVERSITY IN BIOCHEMISTRY 



groups, also modify the electric field and the shape of the macromolecule. 

 Heavy metals, which form coordination complexes with certain groups, 

 act in the same way. In many cases this denaturation and change in shape 

 is accompanied by a tendency to pass into a fibrous state and at the same 

 time certain functional groups which were hidden in the interior of the 

 molecule are revealed. The uncovering of these groups certainly plays a 

 part in the tendency displayed by denatured proteins to form aggregates. 

 The formation of these aggregates and the accompanying decrease in 

 solubility are facilitated at the isoelectric point since then nothing prevents 

 the molecules from coming together. 



Denaturation may be irreversible. This is the case when important 

 changes in structure have taken place altering the geometry of the electric 

 field of the globular molecule. 



Irreversible denaturation may be accompanied by polymerization and a 

 fall in solubility. The appearance of a precipitate is called flocculation; if 

 the precipitate is practically insoluble it is called a coagulum. 



Denaturation may be reversible, if the changes in structure are slight. 

 When the initial conditions are restored, the electrostatic field reestablishes 

 the original shape of the globular molecule. 



B. The Nature and Positions of the Constituent Amino Acids in 



THE Protein 



{a) Nitrogen and Sulphur Content 



One of the present tasks of biochemistry is the determination of the 

 order in which the amino acids are assembled in the protein polypeptide 

 chains and the description of the structure of that protein. It is first of all 

 necessary to know the total protein nitrogen (around 16%) and the total 



