iv OTHER UNKINGS OF AMINO-ACIDS 147 



fact that albumins are pluri-acid bases. If an albumin resulted simply 

 from a linking together of many amino-acids into one chain, we might 

 expect it to be monobasic and monoacid, as are the simple amino- 

 acids. This is, however, not the case. Determinations of the acid 

 capacity by Erb 1 and others (Chapter V., p. 177) show that the 

 equivalent weight of albumins is very low. Thus Erb estimates the 

 equivalent weight of egg-albumin as not exceeding 152, while the 

 molecular weight according to Hofmeister 2 is 5378 or a multiple of 

 this number. Therefore egg-albumin must be at least a 35-acid base. 



The terminal groups in the albumin -molecule are represented 

 especially by the * aminonitrogen,' but also by the NH 9 -groups of 

 lysin and arginin. The second and third N-atom of histidin are 

 also joined in a ring-like formation (see p. 43). According to Eossel 3 

 the basicity of albumins increases in proportion to the increase in the 

 amount of di-amino-acids. 



It is questionable whether the NH 2 -groups of ammonia, arginin, 

 and lysin suffice to explain the high numbers of Erb. They do not 

 suffice in the case of edestin and the hetero-albumose, where calculations 

 can be made with a fair amount of accuracy. That the numerous 

 basic groups of albumins are not of the same value will be shown later 

 on, when discussing the salts of albumins (Cohnheim). 



The power which albumins possess of combining with bases has 

 been measured much less accurately than their capacity for acids ; still 

 here again the equivalent weights of albumins are very much lower 

 than are the lowest possible molecular weights, and therefore albumins 

 must also be pluri-basic acids. This has been proved by Pemsel and 

 Spiro, 4 Laqueur and Sackur, 5 and others. Apart from the a-amino- 

 groups, free carboxyl-groups are met with in glutaminic and in aspartic 

 acids. Cohnheim draws attention to the interesting analogy, seen in 

 octaspartic acid, which, according to Schiff, 6 has this constitution : 



CO CO CO CO CO CO CO COOH 



l\l\l\ \l\l\l\l 

 NELCH NHCH NHCH NHCH NHCH NHCH NHCH NHCH 



I I I I I I I I 

 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 



COOH COOH COOH COOH COOH COOH COOH COOH 



1 W. Erb, Zeitschr.f. Biol. 41. 309 (1901). 



2 F. Hofmeister, Zeitschr.f. physiol. Chem. 24. 158 (1897). 



3 A. Kossel, Ber. d. deutsch. chem. Ges. 34. III. 3214 (1901). 



4 W. Pemsel and K. Spiro, Zeitschr. f. physiol. Chem. 26. 233 (1898). 



5 B. Laqueur and 0. Sackur, Hofmeister s Beitrdge 3. 192 (1903). 



r H. Schiff, Luting's Annalen, 303. 183 (1898), 307. 231 (1899), 31O. 301 (1899). 



