PEPSINUM 537 



PEPSINUM 



(Pepsin) 



Source, &C.- Commercial pepsin is a mixture of the enzyme pepsin 

 with other substances, obtained from the mucous membrane lining 

 the stomach of the pig, sheep, or calf. 



The surface of this mucous membrane exhibits multitudes of minute 

 pits, each of which is about 0'2 mm. in diameter, and is the common 

 orifice of two or three minute, elongated, tubular ducts. The pit 

 together with the ducts debouching into it is termed a gastric gland. 

 The duct is lined with two kinds of cells, viz. central cells and parietal 

 cells, the former being the more numerous. The central cells secrete 

 substances termed zymogens which are the precursors of enzymes 

 but are not the enzymes themselves, the zymogens comprising 

 pepsinogens and rennin zymogen. The pepsinogen is converted into 

 pepsin and the rennin zymogen into rennin. The parietal cells 

 secrete hydrochloric acid. These substances, probably with others, 

 in aqueous solution constitute the gastric juice which is discharged 

 from the glands into the stomach when meat is introduced into the 

 mouth and masticated. Their action on the food is to convert in- 

 soluble proteids into soluble peptones and thus permit of digestion. 

 Peptones differ from (soluble) proteids in not being coagulated by 

 heat or precipitated by nitric acid, &c. 



Commercial pepsin is obtained by stripping the mucous mem- 

 brane from the stomach, mincing it and digesting it with water 

 acidified with hydrochloric acid by which insoluble proteids are 

 dissolved. From the filtered liquid it is precipitated by saturation 

 with sodium chloride or ammonium sulphate, the peptones being left 

 in solution. The pepsin is collected, dissolved in water and freed 

 from sodium chloride, &c., by dialysis ; it may then be precipitated 

 by alcohol, or the aqueous solution may be evaporated to dryness in 

 a vacuum and powdered. 



Description. Pepsin occurs in commerce as a pale yellowish 

 powder, or in translucent scales or grains with a faint odour free 

 from putrescence and a slightly saline bitterish taste. It is soluble 

 in water, especially on the addition of a little hydrochloric acid. It 

 contains the enzyme, pepsin, but does not consist of it. An acidified 

 aqueous solution converts insoluble proteids into soluble parapeptone 

 (or acid albumose), propeptone, and finally into peptone. Its action 

 is inhibited by sodium chloride and by alcohol, and is completely 

 destroyed at a temperature of 70. 



Uses. It is employed in dyspepsia caused by deficient gastric 

 secretion. 



