422 



SCIENCE 



[N. S. Vol. XXVIII. No. 718 



Globulins are commonly described as 

 proteins that are coagulated by heat. This 

 is doubtless true of the globulins of seeds 

 if sufficient acid is present in their solu- 

 tions. It is, however, difficult to add to 

 the saline solutions of most seed globulins 

 a sufficient amount of acid to cause com- 

 plete coagulation on heating, for even a 

 very minute quantity of acid in a strong 

 saline solution alone precipitates a large 

 quantity of the globulin. 



The deportment of edestin in this respect 

 is well illustrated by the experiments of 

 Chittenden and Mendel,^ who showed that 

 a saline solution of edestin was only pai-tly 

 coagulated by boiling, that the edestin re- 

 maining in solution could be recovered un- 

 changed and in well-formed crystals, and 

 that addition of acid to the solution filtered 

 from the eoagulum gave rise to a new 

 coagulum on again heating. 



2. Prolamins^ form a unique and 

 sharply differentiated group of proteins 

 which occur in quantity in the seeds of 

 cereals, but not in those of any other plant 

 yet examined. These are soluble in all 

 proportions in alcohol of 70-80 per cent., 

 and are not aft'ected by boiling their alco- 

 holic solutions, even for a long time. They 

 are practically insoluble in water and 

 saline solutions, but are soluble in dilute 

 solutions of acids and alkalies. 



The prolamins are better characterized, 

 from a chemical standpoint, than any of 



- Chittenden and Mendel, Journal of Physiology, 

 XVII., p. 48, 1894. 



'^ I propose this name for the group -which 

 heretofore has been simply called alcohol-soluble 

 proteins. The name refers to the relatively large 

 proportion of proline and amide nitrogen -which 

 they yield on hydrolysis. The English committee 

 on protein nomenclature has very recently pro- 

 posed to call these proteins gliadins, but as this 

 name has long been used to specifically designate 

 the prolamin obtained from -wheat it seems to me 

 important to have a distinctive name for this 

 group. 



the other groups of seed proteins, for on 

 hydrolysis they all yield a very small 

 amount of arginine and histidine and no 

 lysine whatever. On the other hand, they 

 yield from 20 to 30 per cent, of their total 

 nitrogen in the form of ammonia and also 

 contain relatively large amounts of gluta- 

 minic acid. Gliadin from wheat and rye, 

 and the related hordein from barley, yield 

 about 37 per cent, of glutaminic acid, 

 which is very much more than that found 

 in any other protein yet examined, and 

 zein juelds nearly 20 per cent., which places 

 it among the proteins relatively rich in this 

 amino-acid. 



Prolamins have been found in the seeds 

 of all the cereals examined in my labora- 

 tory, namely — oats, wheat, maize, rye, 

 barley and sorghum. That this form of 

 protein is characteristic of the seeds of all 

 grasses is rendered improbable by the re- 

 cent report of Rosenheim and Kajiura,* 

 who found none in rice. A detailed state- 

 ment of their results, however, has not, to 

 my knowledge, yet been published. 



3. Gliitelins constitute a large part of 

 the proteins of all the cereals that have 

 been studied, and possibly occur in seeds 

 of other kinds. These proteins are " in- 

 soluble in all known neutral solvents, but 

 are easily dissolved by very dilute acids 

 or alkalies. Only one member of this 

 group is known which is accessible to satis- 

 factory investigation. This is the glutenin 

 of wheat which forms nearly one half of 

 the gluten. Owing to the fact that 

 glutenin can be separated from the other 

 components of the seed as a constituent of 

 the gluten, it is possible to make prepara- 

 tions of it of a fair degree of purity. 



As the seeds of the other cereals yield 

 no coherent gluten, the protein correspond- 

 ing to glutenin can not be isolated from 

 them, for the alkaline extracts of these 



* Rosenheim and Kajiura, Journal of Physiol- 

 ogy, XXXVI., p. liv, 1908. 



