30 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



amount of tryptophan in lactalbumin is most noticeable. Greater 

 amounts of tryptophan were present in carcinoma than in the normal 

 tissue, but tryptophan was absent in carcinoma of the breast. 



3. Tryptophan is decomposed by putrefactive bacteria with the 

 formation of indole. An investigation by Herzfeld [1913, i] into the 

 formation of indole by the action of alkali (the highest yields being 

 given by boiling with 1000 c.c. of 9 per cent, caustic soda and I gram 

 of copper sulphate), showed that the estimation of tryptophan under 

 these conditions was not practicable. Sanders and May [1912-13] 

 have also tried to estimate tryptophan by the formation of indole. 

 The pancreatic digest of protein was inoculated with faecal bacteria, 

 distilled, and the indole in the distillate treated with nitrous acid. 

 At the same time an indole solution was treated in a similar way and 

 the colours compared. Caseinogen gave an amount of indole cor- 

 responding to I -6 per cent, of tryptophan. 



4. Herzfeld [191 3, 2] determined the tryptophan content of several 

 proteins by the colorimetric and spectrophotometric comparison of 

 the colour given by tryptophan with /-dimethylaminobenzaldehyde 

 and concentrated hydrochloric acid. A blue colour is given by this 

 reagent with one part of tryptophan in 1 ,000,000. As a standard 

 colour a solution of I gram of ignited copper sulphate dissolved in 

 100 c.c. of water is used, I c.c. of this solution being treated with 20 c.c. 

 of ammonia and diluted to 100 c.c. This blue solution has the same 

 colour as O'OOOI gram of tryptophan in its reaction with /-dimethyl- 

 aminobenzaldehyde and hydrochloric acid. The two are carefully 

 compared before use. About I gram of the purified and dried protein 

 is accurately weighed out and dissolved in 500 c.c. ofo'5 per cent, 

 sodium carbonate solution to which 0-5 gram of pancreatin is added. 

 The solution is kept at 37 in the presence, of chloroform and xylene. 

 50 c.c. are then taken and treated with 10 c.c. of /-dimethylamirio- 

 benzaldehyde solution 1 and 40 c.c. of concentrated hydrochloric acid. 

 After thirty minutes' standing the blue colours are compared. The 

 tryptophan content of the pancreatin is also determined and the 

 amount deducted from the digest of protein with pancreatin. The 

 colorimetric values agreed closely with the spectrophotometric. 



The tryptophan content of several proteins was determined : 



1 20 grams /-dimethylaminobenzaldehyde dissolved in 500 c.c. cone. HC1 and 500 c.c. 

 water. 



