CLASSIFICATION OF VEGETABLE PROTEINS 9 



2. SECONDARY PROTEIN DERIVATIVES. 

 (a) Proteases. 



The first observation which indicated the presence of proteoses in 

 seeds was made in 1879 by Vines (561, 562), who obtained a proteose- 

 like product from lupine-seeds which he called " hemialbumose ". He 

 also noted the presence of a similar substance in the seeds of vetch, 

 hemp and flax. Schulze and Barbieri (485) soon afterwards examined 

 a number of different parts of many kinds of plants, and concluded from 

 the results which they obtained that plant juices and extracts often 

 contain " peptone " (proteose ?) in small quantity. Even during ger- 

 mination they found but a small quantity of "peptone," and stated 

 that a storing up of this substance does not occur. They confirmed an 

 earlier observation of Kern (186), made on lucerne and vetch hay, that 

 plants contain ferments which peptonise protein during extraction. 

 Proteoses have been frequently found in the extracts of seeds after the 

 other proteins had been removed. Whether these proteoses were 

 original constituents of the seeds or resulted from the action of proteo- 

 lytic enzymes is still an open question, for it is extremely difficult to 

 conduct the extraction of the seed and separation of the other proteins 

 in such a way as to certainly exclude the formation of proteoses. 

 That changes occur in seed extracts is shown by many facts already 

 recorded. Osborne (301) found that the extract of the flax-seed 

 yielded a nearly constant quantity of diffusible non-protein nitrogen 

 during several days' dialysis. The fact that the nitrogen diffused 

 during the first dialysis period was only about one-half of that diffused 

 during the subsequent periods, which were equally long, is evidence 

 that the diffusible nitrogen did not exist as such in the seed but 

 was formed from some other substance, presumably protein. Experi- 

 ments recently made by the writer have also shown that more non- 

 protein nitrogen is found in the diffusate from extracts of the seeds of 

 Phaseolus made at 20 than from extracts made with solvents heated 

 to 70. 



That the proteins in many extracts undergo changes in the process 

 of purification is shown by the constant loss of material which is so 

 frequently met with. A striking instance of this was encountered by 

 Osborne and Harris (356), who subjected 600 grammes of crude con- 

 glutin from the yellow lupine to fractionation with ammonium sulphate 

 and finally separated the different fractions by dialysis. Although the 

 mechanical losses during these operations were small, only 314 grammes 



