ALBUMINS OR PROTEINS. 177 



A glance at the composition of the different kinds of proteins shows that 

 they all, with the exception of the protamines, contain the same funda- 

 mental constituents. Occasionally one or another amino acid is absent; 

 thus, glycocoll does not occur in egg- or serum-albumin; lysine is absent 

 in the plant albumins which are soluble in alcohol; tyrosine and trypto- 

 phane in gelatin. If we compare the relative amounts of the various 

 amino acids occurring in the individual proteins, we notice appreciable 

 differences. This is especially striking if we compare the individual 

 groups. In the first place we notice the varying proportions of the 

 mono- and di-amino acids that go to make up the individual proteins. 

 The latter are very strongly represented in the protamines, and least so 

 among the albuminoids. Between these two extremes we find the com- 

 mon albumins and the histons. Very noticeable is the predominance of 

 special mono-amino acids, e.g., glutamic acid and leucine in the albumins 

 present in the seeds of plants. It constitutes one-third of gliadin. 

 If we compare the individual groups of proteins among themselves, we 

 find in many cases a very general similarity. Thus, glycocoll is absent 

 in egg-albumin and serum-albumin, whereas the globulins invariably con- 

 tain it. We are, therefore, in a position to classify chemically at least a 

 portion of the different proteins. The fact that they all contain the same 

 fundamental constituents makes it easier for us to understand their trans- 

 formations in the animal organism. 



Although the complete hydrolysis of itself serves to give us a fairly 

 comprehensive knowledge of the amino acids participating in the con- 

 struction of the albumins, it, on the other hand, does not give us any idea 

 of the manner in which these substances are united. Until recently it had 

 not been possible to split off complexes from the proteins, and to identify 

 positively individual compounds containing only a part of the total amino 

 acids. We are certainly justified in concluding that the albumoses have a 

 lower molecular weight than the original proteins, and that the peptones 

 are, without doubt, to be considered as still lower cleavage-products. Up 

 to the present time the albumoses and peptones have been grouped almost 

 entirely according to their limits of precipitation and solubility. Only in 

 specific cases have they been characterized by the absence of a definite 

 amino acid, or by an excess of such. Recently M. Siegfried and his 

 students have tried to obtain products by cautious hydrolysis of some 

 of the albuminous substances which would contain only a part of the 

 amino acids occurring in the original protein. Siegfried 1 has described 

 several such products. He calls them kyrines. It is at present impossible 



1 Siegfried: Ber. math-physikal. Kl. klg. sachsischen Gesel. Wiss. Leipzig, Sitzung II. 

 III. p. 63, 1903; Z. physiol. Chem. 38, 259 (1903); 43, 46 (1904); 43, 44 (1904). Cf. 

 also C. Bockel: ibid. 38, 289 (1903). T. R. Kriiger: ibid. 38, 320 (1903). W. Scheer- 

 messer: ibid. 41, 68 (1904). Z. H. Skraup and R. Zwerger: Monatsh. 26, 1403 (1905). 



