202 PHYSIOLOGICAL CHEMISTRY 



3. The Glycyl-tryptophane Reaction. The dipeptide glycyl-tryptophane 1 

 may be used in place of the peptone solution for the demonstration of erepsin. 

 It is claimed to be of service in the diagnosis of gastric cancer. It is claimed that 

 a peptide-splitting enzyme (erepsin) is present in the stomach contents of indi- 

 viduals suffering from cancer of the stomach, whereas the stomach contents of 

 normal individuals contains no such enzyme. The glycyl-tryptophane test, there- 

 fore, may sometimes furnish a means of aiding in the diagnosis of this disorder. 

 As applied to stomach contents, the test is as follows : 2 Introduce about 10 c.c. of 

 the filtrate from the stomach contents into a test-tube, add a little glycyl-trypto- 

 phane and a layer of toluene, and place the tube hi an incubator at 38C. for 24 

 hours. At the end of this time by means of a pipette transfer 2-3 c.c. of the fluid 

 from beneath the toluene to a test-tube, add a few drops of 3 per cent acetic acid 

 and carefully introduce bromine vapors. Shake the tube and note the production 

 of a red color if tryptophane is present. The tryptophane has, of course, been 

 liberated from the peptide through the action of the peptide-splitting enzyme 

 (erepsin) elaborated by the cancer tissue. 



If an excess of bromine is added the color will vanish. If no rose color is 

 noted, add more bromine vapors carefully with shaking until further addition of 

 the vapors causes the production of a yellowish color. This indicates an excess 

 of bromine and constitutes a negative test. Occasionally the rose color indicating 

 a positive test is so transitory as to escape detection unless the test be very care- 

 fully performed. 



Several fallacies have been pointed out in connection with this test. 

 In the first place the regurgitation of duodenal contents through the 

 pylorus might insure the presence in the stomach of erepsin and trypsin 

 either of which possesses peptide-splitting power. It has also been 

 claimed that saliva contains an enzyme capable of splitting glycyl- 

 tryptophane. Doubt has, however, been cast upon the dipeptide- 

 splitting agent of the saliva by Smithies 3 and by Jacque and Woodyatt, 4 

 who point to bacteria as the peptolytic agents. In any event saliva 

 contains something which is capable of splitting the glycyltryptophan, 

 thus making the entrance of saliva into the stomach an important 

 source of error, so far as the utility of this test is concerned, as a diagnos- 

 tic aid. Bacteria may, of course, be removed from the gastric juice by 

 passing the fluid through an effective filter. 



EXPERIMENTS ON INVERTASES 5 



i. Preparation of an Extract of Sucrase. Treat the finely divided epi- 

 thelium of the small intestine of a dog, pig, rat, rabbit, or hen with about 3 

 volumes of a 2 per cent solution of sodium fluoride and permit the mixture to 



x This dipeptide is sold commercially under the name "Ferment Diagnosticon." 

 Neubauer and Fischer: Deutsches Archivf. klinische Medizin, 97, 499, 1909. 

 'Smithies: Arch. Int. Med., 10, 521, 1912. 



4 Jacque and Woodyatt: Arch. Int. Med., Dec., 1912, p. 560. v 



6 "The Inverting Enzymes of the Alimentary Tract," Mendel and Mitchell: American 

 Journal of Physiology, 20, 81, 1907-08. 



