332 PROTEINS 



in regard to the two essential features of this group, 

 namely, solubility in water and coagulation by heat, they 

 differ in regard to their behaviour towards strong solutions 

 of inorganic salts. Thus animal albumins are not sup- 

 posed to be precipitated by half saturation with ammonium 

 sulphate or saturation with sodium chloride or magnesium 

 sulphate, but this is not always found to be the case for 

 vegetable proteins, many of which are precipitated under 

 these conditions. 



Globulins. These are exemplified by serum globulin, fibrinogen, 

 and myosinogen, and also the derivatives of the two latter, 

 fibrin and myosin. Examples of vegetable globulins are 

 furnished by conglutin from the seeds of Lupinus, edestin 

 from the seeds of Cannabis sativa, excelsin from the seeds 

 of Bertholletia excelsa, legumin from the seeds of Pisum 

 sativum, Vicia Faba, and other Leguminosae, juglansin 

 from the seeds of Juglans spp., vicilin from the seeds of 

 Pisum sativum, Vicia Faba^ etc., and vignin from the 

 seeds of Vignd sinensis. In brief, globulins are amongst 

 the commonest protein reserves of the higher plants. 



The typical globulins are insoluble in pure water and 

 are coagulated by heat. They are soluble in dilute salt 

 solutions, but are insoluble in stronger salt solutions ; thus, 

 unlike the albumins, they are precipitated by saturation 

 with magnesium sulphate or by only half saturation with 

 ammonium sulphate.* 



The vegetable globulins, which form the major portion 

 of the reserve proteins of all seeds except cereals, do not 

 always conform to these conditions of solubility. Thus, 

 whereas animal globulins are insoluble in water and are 

 precipitated by half saturation with ammonium sulphate, 

 a great many globulins from plants are precipitated at 

 less than half saturation, and, on the other hand, some are 

 not precipitated until the solution is almost saturated with 



* These differences in solubilities between albumins and globulins may be 

 illustrated by dissolving some of the white of an egg in water and placing it in a 

 dialyser ; as the small quantity of sodium chloride contained in the egg-white 

 diffuses out, the globulin is precipitated out of solution ; or again, if the solution is 

 mixed with an equal volume of saturated ammonium sulphate solution, the globu- 

 lin will likewise be precipitated out, owing to the solution now being half saturated 

 with ammonium sulphate, but the albumin will remain in solution. 



