Sect. V, 1922 [71] Trans. R.S.C. 



XII. The Progress of Tryptic Digestion of Protein as Studied by the 

 Method of Butyl Alcohol Extraction (Preliminary Communication) 



By Andrew Hunter, M.A., F.R.S.C. 



(Read May Meeting, 1922) 



An approximately 10% solution of sodium caseinate was sub- 

 mitted, in portions of 250 c.c, for varying intervals to the action of a 

 commercial preparation of trypsin. Each portion, at the end of its 

 prescribed period of digestion, was heated to boiling, diluted till the 

 separated tyrosine had dissolved, cooled, and made up to 1,000 c.c. 

 The total and amino nitrogen were then determined in suitable small 

 aliquots. The residue was concentrated, filtered from tyrosine, and 

 extracted with butyl alcohol, according to the method of Dakin,^ 

 for a total period of 48 hours. In this way the product of digestion 

 was separated into three fractions, corresponding to those obtained 

 by similar treatment of a completely hydrolyzed protein. The total 

 and amino nitrogen of each fraction was determined. The data thus 

 obtained were in each case calculated to the common basis of 100 gms. 

 of nitrogen in the total digest; and in this form are collected in the 

 table. The figures there included as representative of complete 

 hydrolysis are calculated from the best available data concerning 

 the composition of casein,- and with the assumption that it Contains 

 2.2% of tryptophane^ 



The experiments were undertaken primarily with the idea of 

 throwing additional light, by a convenient method, upon the rate 

 and order of liberation of the monoamino-monocarboxylic acids, 

 which are extracted by butyl alcohol but precipitated in the extraction 

 flask. It will be seen (columns 8-10) that the fraction containing 

 these acids increases steadily, as was to be expected, with the progress 

 of digestion. The percentage of amino nitrogen in this fraction is, 

 moreover, such as to show that it does essentially consist of monoamino 

 acids in the free state. These can be completely purified, it has been 

 found, by re-solution and re-extraction with butyl alcohol; but this 

 procedure is accompanied by considerable loss. The figures as they 

 stand probably represent, not quite accurately yet fairly closely, the 

 actual rate of liberation of the monoamino-monocarboxylic acids as 



iH. D. Dakin: Biochem. Journ., xii, p. 290 (1918). 

 ^F. W. Foreman: Biochem. Journ., xiii, p. 378 (1919). 

 'Fiirth and Lieben: Biochem. Zeitschr., cix, p. 124 (1920). 



