638 PHYSIOLOGICAL CHEMISTRY. 



tive state, and are then spoken of as zymogens or pro-enzymes. These 

 zymogens become active in the presence of certain supplementary 

 substances. These substances are called kinases if of organic nature, 

 and activators if of inorganic nature. Thus, enterokinase is the kinase 

 of trypsinogen, converting it into trypsin, while hydrochloric acid is 

 the activator of pepsinogen, converting it into pepsin. 



While enzymes will be fully considered later, the following two 

 are mentioned here because they furnish official preparations. 



Pepsin is one of the active principles of gastric juice, capable of 

 converting albumin, in the presence of hydrochloric acid, into soluble 

 peptones. While pure pepsin is not known, a number of preparations 

 containing more or less of this ferment are sold as pepsin. They are 

 obtained by dhTerent processes of extraction from the glandular layer 

 of fresh stomachs from healthy pigs. 



Pepsin, U. S. P., should be either a fine, white, or yellowish-white, 

 amorphous powder, or consist of thin, pale yellow or yellowish, 

 transparent or translucent grains or scales. It should be capable 

 of digesting not less than 3000 times its own weight of freshly 

 coagulated and disintegrated egg albumin. 



Experiment 72. Use the U. S. P. process for the valuation of pepsin, as fol- 

 lows : " Mix 9 c.c. of diluted hydrochloric acid with 291 c.c. of distilled water, 

 and dissolve the pepsin in 150 c.c. of the acid liquid. Immerse a hen's egg, 

 which should be fresh, during fifteen minutes in boiling water ; remove the 

 pellicle and all of the yolk ; rub the white, coagulated albumin through a clean 

 No. 40 sieve. Reject the first portion that passes through the sieve, and place 

 10 Gin. of the succeeding portion in a wide-mouthed bottle of 100 c.c. capacity. 

 Add 20 c.c. of the acid liquid, and with the aid of a glass rod tipped with cork 

 or black rubber tubing, completely disintegrate the albumin ; then rinse the rod 

 with 15 c.c. more of the acid liquid and add 5 c.c. of the solution of pepsin. 

 Cork the bottle securely, invert it three times, and place it in a water-bath that 

 has previously been regulated to maintain a temperature of 52 C. (125.6 F.). 

 Keep it at this temperature for two and one-half hours, agitating every ten 

 minutes by inverting the bottle once. Then remove it from the water-bath, 

 add 50 c.c. of cold distilled water, transfer the mixture to a 100 c.c. graduated 

 cylinder, and allow it to stand for half an hour. The deposit of undissolved 

 albumin should not then measure more than 1 c.c. 



"The relative proteolytic power of pepsin stronger or weaker than that just 

 described may be determined by ascertaining through repeated trials the 

 quantity of the above pepsin solution required to digest, under the prescribed 

 conditions, 10 grammes of boiled and disintegrated egg albumin. Divide 15,000 

 by this quantity expressed in c.c. to ascertain how many parts of egg albumin 

 one part of the pepsin will digest." 



Pancreatin, U. S. P. This preparation is a mixture of the 

 enzymes existing in the pancreas of warm-blooded animals, and is 



