214 Hydrolysis of the Soluble Protein of Swede Turnips 



together with the picrate method for separating glycine and alanine, 

 and the lead method for separating vahne and the leucines, make it 

 possible now to determine these five amino-acids with a fair degree of 

 accuracy. 



All the plant proteins for which hydrolyses have been published 

 have been prepared from seeds ; tuberini seems to be the only protein 

 yet prepared from a vegetative organ, and no hydrolysis has been 

 pubhshed for it. Osborne has pointed out^ that as these seed 

 proteins appear externally and are lost to the plant and can take no 

 further part in the metabolism, they are to be regarded as excretory 

 substances. These reserve or excretory proteins, whether of plants 

 or of animals, often yield a very high percentage of one or more amino- 

 acids on hydrolysis. Thus ghadin of wheat and hordein of barley 

 yield over 36 per cent, of glutaminic acid, while silk fibroin yields 

 36 per cent, of glycine and 21 per cent, of alanine. The alcohol 

 soluble seed proteins yield the basic amino-acids in very small amount ; 

 lysine indeed is almost invariably absent. 



No such wide differences have been found among the physiologically 

 active proteins, the protamines excepted. They are always more equally 

 balanced in their amino-acid content. 



The protein which has been studied here has been prepared from a 

 vegetative organ, and must be regarded as physiologically active. It 

 shows no excessive content of any particular amino-acid and all the 

 usual "Bausteine" are present. 



Practically all the vegetable proteins already studied contain from 

 10 to 50 per cent, of glutaminic acid; in this case we have only 3-18 

 per cent. Nearly all protein hydrolyses give much more glutaminic 

 acid than aspartic acid; in this case we find twice as much aspartic 

 acid as glutaminic acid. 



It will be interesting to see how far the figures given at present for 

 the dibasic acids will have to be altered when Foreman's new method 

 is apphed to some of the well-known proteins. The poor yield of aspartic 

 acid obtained by the ester method is well known ; Hopkins and Savory^ 

 obtained much more aspartic acid by direct precipitation from Bence- 

 Jones' protein than by the ester method. The difficulty of obtaining 

 any glutaminic acid as the hydrochloride when less than 10 per cent, 

 is present is also well known. These imperfections in the methods of 



' Osborne and Campbell. J. Amer. Chem. Soc. 1896, xvin, .575. 

 - Monographs on Biochemistry. The Vegetable Proteins, p. 9. 

 3 Journ. Phymol. XLii, 189, 1911. 



