ORGANIC CHEMISTRY 23 



Salts of heavy metals. 



Heating to various temperatures above 30 C. 

 The following classification indicates the nature of the 

 various protein substances.* 



1. Protamines. Simple basic substances mainly derived 

 from fish-sperm. 



2. Histones. Slightly more complex substances preci- 

 pitated by ammonia. This and the preceding class merge 

 into each other. 



3. Albumins. Proteins which dissolve in distilled water 

 and are coagulated by heating. 



4. Globulins. These like albumins are coagulated by heat 

 but they do not dissolve in distilled water and they are 

 more readily precipitated from their solutions by salts. 



5. Glutelins. Alkali soluble proteins of vegetable origin. 



6. Gliadins. Vegetable proteins soluble in alcohol of about 

 70 per cent, concentration. 



7. Sdero-proteins. Substances of skeletal origin usually 

 insoluble in water. 



8. Phospho-proteins. These contain phosphorus which is 

 easily separated by alkali in the form of phosphoric acid. 



9. Conjugated proteins in which a ''prosthetic" group is 

 united to the protein molecule. 



(a) Nucleo-proteins containing phosphorus in the form 

 of nuclein. 



(b) Gluco-proteins containing a carbohydrate group. 



(c) Chromo-proteins giving rise to coloured substances. 



10. Protein derivatives. Substances formed during the 

 hydrolysis of proteins. 



(a) Metaproteins. Substances insoluble at the neutral 

 point but soluble in either acid or alkali. These, like 

 most of the intact proteins, give a purple colour with 

 copper sulphate and alkali. 



(b) Proteoses. These give a pink colour with copper 

 sulphate and alkali and are precipitated from their 

 solution by salts. 



(c) Peptones. These give a pink colour with copper 

 sulphate and alkali, but are not precipitated from their 

 solution by salts. 



(d) Polypeptides. These give a blue colour with copper 

 sulphate and alkali. They are comparatively simple sub- 

 stances composed of a few amino acids linked together. 



* Proc. Physiol. Soc. Journ. Physiol., 1907, vol. 35, pp. xvii-xx and 

 1908, vol. 37, pp. xxxii-xxxiv. 



