RESULTS OF ANALYSIS 69 



Methylation of Amino Acids. 



A method which may prove of some service in separating these 

 various mixtures was described by Engeland [1909]. The amino acids 

 are methylated in alkaline solution with methyl iodide and converted 

 into their betaines : 



CH 2 .NH 2 CH 2 .N-CH 3 



+ 3CH 3 I + 3 NaOH = 3 NaI + 3 H 2 O + | " | \CH 3 

 COOH CO O 



These products are separated by means of their double salts with 

 mercuric chloride, gold chloride, and platinum chloride. In the case 

 of caseinogen, Engeland isolated (i) 1-methyl-hygric acid, which is de- 

 rived from proline ; a yield corresponding to 67 per cent, of proline 

 was obtained ; (2) trimethyl leucine, (3) trimethyl valine, (4) betairie, 

 (5) trimethyl-alanine. Subsequently, Engeland [1910] prepared the 

 trimethyl derivative of phenylalanine and dimethyl glutamic acid, and 

 [1914] isolated methyl-hygric acid from the products of hydrolysis of 

 spongin. The procedure adopted was very laborious and seems to 

 offer no advantages over the ester method. Its chief use may be in 

 the separation of those mixtures which result by the ester method and 

 for which the methods at present in use are not so satisfactory. 



B. 



The data in our possession show definitely that the various proteins 

 are composed of the same units ; in some cases certain are missing 

 and in other cases one or more units are present in very much larger 

 amount. These differences on the whole confirm our classification of 

 the proteins on physical properties. No great differences are notice- 

 able between the members of any single group except in the case of the 

 scleroproteins. Although two proteins in any group may contain the 

 same amount of any unit we cannot say that they are identical. Even 

 if they contained the same amount of all the units they might still be 

 different, for the arrangement of the units in the molecule may not 

 be the same. The analytical data are given on pp. 111-130. The 

 following brief particulars may be noted : 



