PEPSIN. 467 



the mucous membrane, cannot, according to HAMMARSTEN, either be the 

 only or the most prominent peptic enzyme of the pyloric part. According 

 to GLAESSNER, it also acts in neutral and alkaline reaction and yields 

 tryptophane among other cleavage products. According to BERGMANN l 

 it is identical with erepsin (see below). Among the enzymes of the 

 mucosa of the stomach belongs the so-called antipepsin discovered by 

 WEiNLAND, 2 which has a retarding action upon pepsin digestion and, 

 as some claim, prevents the self-digestion of the mucous membrane. 



Pepsin is as difficult to isolate in a pure condition as are other 

 enzymes. The pepsin prepared by BRUCKE and SUNDBERG gave negative 

 results with most reagents for proteins, and showed nevertheless a 

 powerful action, which seems to indicate that it was very pure. SCHOU- 

 MOW-SiMANOWSKi, NENCKi and SIEBER, have designated as the true 

 enzyme the substance containing chlorine, which they obtain by strongly 

 cooling the gastric juice. That this precipitate is not a chemical indi- 

 vidual, and hence cannot be pepsin, follows from the investigations of 

 PEKELHARING. While pepsin, according to NENCKI and SIEBER, was 

 rich in phosphorus and contained nucleoprotein, PEKELHARING'S pepsin 

 was free from phosphorus and yielded no nucleoprotein. FRIEDENTHAL 

 and MiYAMOTA 3 have also shown that the pepsin is still active after 

 the splitting off of the nuclein complex (and also the protein). As pepsin 

 is readily precipitated with the proteins and combines therewith, it is 

 difficult to decide whether pepsin is a protein substance or not, and the 

 question as to its nature is still undecided, just as is the case with other 

 enzymes. As ordinarily known, pepsin, at least in an impure form, is 

 soluble in water and glycerin. It is precipitated by alcohol, but is only 

 slowly destroyed thereby. In aqueous solution its action is quickly 

 destroyed on heating to boiling. According to BiERNACKi 4 pepsin 

 in neutral solutions is destroyed by heating to 55 C. In the dry state 

 it can be heated to over 100 C. without losing its activity. In the 

 presence of 2 p. m. HC1 a temperature of 55 C. is not injurious, and the 

 compound with acid is more resistant than the free pepsin (GROBER 5 ) . 

 Pepsin in acid solution is destroyed by heating to 65 C. for five minutes. 



1 Glaessner, Hofmeister's Beitrage, 1; Klug, Pfliiger's Arch., 92; Reach, Hofmeis- 

 ter's Beitrage, 4; Pekelharing, Arch, des scienc., biolog., St. Petersbourg 11; Pawlow- 

 Festband, 1904; Bergmann, Skand. Arch. f. Physiol., 18. 



2 Zeitschr. f. Biologic, 44. 



3 Briicke, Wien. Sitzungsber,. 43; Sundberg, Zeitschr. f. physiol. Chem., 9; Schou- 

 mow-Simanowski, Arch. f. exp. Path. u. Pharm., 33; Pekelharing, Zeitschr. f. physiol. 

 Chem., 22 and 35; Nencki and Sieber, ibid., 32; Friedenthal and Miyamota, Centrabl. 

 f. Physiol, 15, 785. 



4 Zeithschr. f . Biologic, 28. 



8 Arch. f. exp. Path. u. Pharm., 51. 



