70 THE CHEMICAL CONSTITUENTS OF THE BODY 



composition. Yet in none of the analyses of proteid has the ash been taken 

 into account. 



Investigators have subjected proteids to various treatments, particularly 

 hydrolytic cleavage, and have sought to determine the resulting cleavage prod- 

 ucts both qualitatively and quantitatively, hoping thus to arrive at the con- 

 stitution of the proteid molecule. In this way it has been shown that certain 

 groups of atoms are present in all proteid substances, while others occur only 

 in some and are therefore not characteristic of the proteids as a group. Such 

 compounds as contain the smallest number of atomic groups and at the same 

 time give all of the general proteid reactions would be classed by this method 

 as simple proteids. The compound proteids would be formed by addition 

 of new groups of atoms to the simple proteid molecule. 



The atomic groups thus far known as characterizing the proteids are the 

 following (Hofmeister). 



1. The guanidin rest CNH . NH 2 . 



2. Monobasic a-monamino acids of the series C n H 2n+ iNO 2 , such as ammo- 

 acetic acid (glycocoll, CH 2 (NH,) .COOH), amino-propioriic acid (alanin, CH 3 . 

 CHCNH 2 ).COOH), amino-butyric acid (CH 3 .CH 2 .CH(NH 2 ) .COOH), amino- 

 valerianic acid (CH 3 .CH 2 .CH 2 .CH(NH 2 ) .COOH), amino-caproic acid, isobutyl- 

 amino-acetic acid (leucin, (CH 3 ) 2 .CH.CH 2 .CH(NH 2 ) .COOH). Of these com- 

 pounds leucin, glycocoll and alanin occur most abundantly, amino-valerianic 

 acid and amino-butyric acid less frequently. Certain of them are wanting' in 

 various proteids. 



3. Monobasic a-to-diamino acids of the series C n H 2n+2 N 2 O 2 : e. g., the 

 a-8-diamino-valerianic acid (CH 2 (KH 2 ) .CH 2 .CH 2 .CH(NH 2 ) .COOH) and the 

 a-e-diamino-caproic acid (lysin, CH 2 (NH 2 ) .CH 2 .CH 2 .CH 2 . CH(NH 2 ) .COOH). 

 The former is always associated with the guanidin rest, the compound being 



described as arginin: NH= _ CH(m) C 





Arginin and lysin occur in varying proportions in all proteids (Drechsel, Hedin, 

 Kossel), although as an exception one of them may be entirely absent, as lysin 

 from zei'n. They are particularly abundant in the protamins, first obtained by 

 Miescher from fish sperm, and described by Kossel as the simplest proteid. This 

 designation, however, is not admissible since protamins do not contain sulphur. 



4. A monobasic /3-oxy-a-monamino acid, namely, the /3-oxy-a-amino-propi- 

 onic acid (serin, CH 2 (OH) .CH(NH 2 ) .COOH), has been demonstrated so far 

 in serum albumin, globin and edestin, and probably occurs in the other simple 

 proteids, since it was found in casein and in fibroin of silk (Fischer). 



5. A monobasic /3-thio-a-monamino acid: namely, the /3-thio-a-monamino- 

 propionic acid (CH 2 (SH) .CH(NH 2 ) .COOH), corresponding to serin, which 

 probably enters into proteids as the disulphide (cystin, COOH.CH(OTL) . 

 CH 2 -S-S-CH 2 .CH(NH 2 ).COOH) (K. A. H. Morner, Embden). Morner finds 

 that the total sulphur of keratin (cow's horn, human hair), serum albumin, and 

 serum globulin might occur as cystin groups. In the shell membrane of the hen's 

 egg as much as three-fourths of the sulphur are present as cystin, in fibrinogen 

 about one-half, and in egg albumin only about one-third. How the remaining 

 sulphur is combined in these and other proteids, we do not know. 



6. Dibasic a-monamino acids of the series C n H 2n+1 NO4. namely, amino- 

 succinic acid (aspartic acid, COOH. CH,.CH(NH 2 ) .COOH) and amino-pyro- 

 tartaric acid (glutamic acid, COOH. CH 2 .CH 2 .CH(NH 2 ) .COOH). The per- 



