PEPSIN. 443 



acts in neutral and alkaline reaction and yields tryptophane among other 

 cleavage products. According to BERGMANN 1 it is identical with erepsin 

 (see below) . Among the enzymes of the mucosa of the stomach belongs 

 the so-called antipepsin discovered by WsiNLAND, 2 which has a retard- 

 ing 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. SCHOUMOW- 

 SIMANOWSKI, NENCKI and SIEBER, and also PEKELHARiNG,have designated 

 as the true enzyme the substance containing chlorine, which they obtained 

 by strongly cooling the gastric juice. That this precipitate is not a 

 chemical individual, and hence cannot be pepsin, follows from the investi- 

 gations 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. FRIED- 

 ENTHAL 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 there- 

 with, 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 

 BIERXACKI 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. On adding peptone or certain salts the 

 pepsin may be heated to 70 C. for the same time without destruction. 



The behavior of pepsin on heating its acid solution is influenced not 



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

 ter's Beitrage, 4; Pekelharing, Arch, des scienc. hiolog., 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 Zeitschr. f . Biologic, 28. 



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



