COMPOUND PROTEINS 



149 



Elastin, peptone, deuteroalbumose, histopeptone and several 

 peptids fail to yield a precipitate. Upon digestion of these 

 precipitates with pepsin the protamin is set free * and the remain- 

 der of the compound is converted into deuteroalbumose and 

 peptones which are not precipitable by picric acid. The pro- 

 tamin which was held in the compound before digestion can now 

 be determined quantitatively by precipitation with picric acid. 

 The following are among the results which were obtained by 

 Hunter : 



An attempt made by Gay and Robertson (32) to prepare 

 protamin (salmin) caseinate by the method of Hunter failed to 

 yield a product containing the high proportion of protamin which 

 he describes. The nitrogen content of the compound protein 

 indicating a protamin content of less than ten per cent. The 

 origin of this discrepancy has been ascertained by af Ugglas 

 (117) who has shown that the preparations described by Hunter 

 contained a considerable excess of the protamin precipitated in 

 a condition of admixture with the compound. The compound 

 of protamin (clupein) with casein prepared by af Ugglas con- 

 tained 94 per cent of casein and 6 per cent of the protamin 

 while the compound with haemoglobin contained 5 per cent of 

 protamin. Schmidt, who has prepared protamin (salmin) edesti- 

 nate (110) (116), finds that it contains about ten per cent of the 

 protamin. 



When globin and casein are mixed in faintly acid solution 

 (110) a precipitate of globin caseinate is produced which is soluble 

 in excess of acid or in dilute alkalies (103). That this precipi- 

 tation is accompanied by true compound formation has been 

 demonstrated by the method of electrometric titration (Schmidt 



* The protamins, although readily digestible by trypsin, are not digestible 

 by pepsin. 



