A METHOD FOR THE DETERMINATION OF 



TRYPTOPHAN DERIVED FROM 



PROTEIN 



JESSE A. SANDERS and CLARENCE E. MAY 

 (Chetnical Laboratories of Indiana University, Bloomington, Ind.) 



Introduction. Tryptophan is a protein cleavage prodiict that 

 is never obtained abundantly. So far as we know the tryptophan 

 yield has been determined quantitatively in the case of but two 

 proteins, namely casein^ and wheat ghadin.^ Only traces of tryp- 

 tophan can be obtained from other proteins; and some proteins, 

 especially gelatin, fail to yield it, if the indications of the usual test 

 with glyoxyhc acid and sulfuric acid are rehable. 



Although tryptophan cannot be abundantly obtained from pro- 

 teins, considerable importance is attached to it because it is produced 

 in the tryptic digestion of protein and, in putrefaction, yields indol. 

 The quantity of indican in urine indicates, in a general way, the 

 extent of intestinal putrefaction. One usually accepts that con- 

 clusion without considering the details of the tryptophan trans- 

 formation, which involves the necessary presence of tryptophan 

 precursors in the original protein molecules ; the degree of digestion 

 of the particular proteins that yield tryptophan; the conversion of 

 tryptophan into indol rather than skatol ; followed by the absorption 

 of indol, its oxidation to indoxyl, its esterification and its excre- 

 tion in the urine in the form of the potassium ethereal sulfate. 



Owing to the evanescent nature of tryptophan, its Isolation from 

 tryptic digestion mixtures has been the subject of many investiga- 

 tions. Although Hopkins and Cole, Abderhalden, and others, have 



^Abderhalden: Zeit. f. physiol Chem., 190S, xHv, p. 23; Abderhalden and 

 Samuely: Ibid., p. 276. (100 gm. of gliadin yield about i.o gm. of tryptophan; 

 100 gm. of casein yield 1.5 gm. of tryptophan.) 



^ Osborne and Clapp : Amer. Jour. Physiol., 1906, xvii, p. 231; Osborne and 

 Guest : Jour. of Biol. Chem., igii, ix, p. 426. (Hydrolysis of gliadin; revised 

 gliadin-tryptophan figures.) 



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