[hunter] TRYPTIC digestion OF PROTEIN 73 



a group. The problem of separating the group at each stage into its 

 individual constituents will be undertaken in the near future. 



Perhaps the most interesting, and certainly the least expected, 

 feature revealed by the method is that the digestion product has a 

 considerable proportion of its nitrogen in combinations which are 

 soluble in butyl, and also (as was found) in ethyl alcohol. This 

 butyl-soluble fraction (columns 5-7) appears in the experiment 

 reported to increase at first, and later to diminish, as digestion pro- 

 ceeds ; but other experiments have thrown some doubt on the regular- 

 ity of this particular phenomenon. The exact nature of the alcohol- 

 soluble material is yet in doubt. It is certainly a mixture. Its low 

 content of amino nitrogen shows that it does not consist mainly of 

 free amino-acids, though it always contains a little tryptophane and 

 tyrosine. Most of it is precipitable by phosphotungstic acid. In 

 various ways it has been separated into sub-fractions, but I have not 

 yet succeeded in obtaining from it anything which could be demon- 

 strated to be a single substance. Most of the subfractions have one 

 character in common; when hydrolyzed by acid and subjected to a 

 Van Slyke analysis they yield a high proportion of non-amino nitrogen 

 in the "filtrate from the bases." This non-amino nitrogen stands, 

 moreover, always in some simple relation to the amino nitrogen of 

 the filtrate, such as 1 :1 or 1 :2. These facts suggest that the material 

 consists largely of polypeptides (or possibly anhydrides), in the 

 composition of which the proline radicle plays a considerable part. 

 The problem presented by this interesting fraction is, of course, 

 being made the subject of further study; for if it should prove possible 

 to isolate by the Dakin procedure, and then to identify, definite 

 alcohol-soluble products of partial hydrolysis, it would probably add 

 a good deal to our knowledge of protein constitution. 



It might, perhaps, be suspected that the butyl-soluble material 

 is an artefact, produced by the heating together of many amino-acids 

 in an anhydrous medium. There is indeed one circumstance which 

 rather encourages such a suspicion. The last two columns of the 

 table show that while the total nitrogen is nearly all recovered in the 

 various fractions, there is a decided deficit of the amino nitrogen. 

 Some condensation, therefore, of once free amino acids has taken 

 place as a consequence of the butyl alcohol treatment, and it is not 

 impossible that the products of this condensation contribute to the 

 butyl-soluble fraction. Whether this be so or not, the fraction as a 

 whole cannot be produced in such a manner; for (1) if it were, its 

 total nitrogen, added to the amino nitrogen of the other two fractions, 

 should equal the original amino nitrogen of the total digest, whereas, 



