378 



Determination of Tryptophan 



[April 



days. It contained indol and was alkaline in reaction. Of i liter 

 of distillate obtained by steam distillation, each 50 c.c. contained the 

 quantity of indol present in 2.0 c.c. of the Standard Solution, in- 

 dicating that the indol in the putrefactive mixture amounted to lo.o 

 mg. A summary of the analytic data is appended. 



The yield of indol could be derived from 1.7872 gm. of trypto- 

 phan in the case of sample C and from 1.7436 gm. of tryptophan in 

 the case of sample D. The weight of casein corresponding to the 

 amount of indol found must have yielded the calculated weight of 

 tryptophan. This being the case, 100 gm. of casein yield either 

 1-593 g"^- of tryptophan (C) or 1.633 g"^- of tryptophan {D), as 

 the minimum amounts. 



Hopkins and Cole claim that intestinal bacteria form small 

 amounts of indol-acetic acid and other indol-containing substances, 

 but we have not found these in our putrefactive mixtures, although 

 they may have been formed in very small amounts, f or which reason 

 we give the two results as indicating the minimum amounts of indol- 

 yielding radicals in casein. Our results are as high as those ob- 

 tained by other investigators. It is likely, of course, that the 

 method will be improved by the further study we hope to give it, 

 especially in its application to other common proteins. The present 

 paper presents only preliminary results. 



The method, as outlined, is slow but it promises to be a satis- 

 factory process for the determination of one of the cleavage 

 products of protein material that hitherto has been difficult to de- 

 termine quantitatively. 



