THE BIOl III. MH \1. PROI OP DIGEE HON 



ess is the same for each of these enzymes, [ndeed, there is considerable 

 evidence thai pepsin does not, like the other enzymes, break up the 

 chain of amino acids thai are linked together to compose the polypep- 

 tides, bul thai it only splits the big molecule of albumin or globulin 

 into several large groups, each of which is composed of long ami 

 chains. Its action appears to be analogous with thai of amy', 

 starch, by which, it will be remembered, the l>iu r polysaccharide m 

 cule is split inio smaller polysaccharide molecules, which then become 

 attacked by the dextrinase and split into disaccharide moleculi 

 page 656). The evidence in support of this view is: l thai pepsin is 

 unable to dip-si polypeptides, and (2 thai it is able to digec tain 



proteins upon which erepsin (see page 490) lias no action. 



The hydrolytic splitting <>f large into smaller protein molecules, like 

 thai by which the chains of amino acids in the polypeptides bse- 



quently broken up, consists in a breaking of amino-carboxyl linkings 

 (NHCO see page ">! ,v . with the consequenl liberation of a large num- 

 ber of unattached amino groups. The number of these free amino groups 

 ••an be determined quantitatively by the formaldehyde titration method 

 (if Sorensen.* By this method it can be shown that from the very start 

 of peptic digestion the number of free annuo groups increases, and | 

 passu the power of the digestive products t< mbine with free hydro- 

 chloric acid. Indeed, when the experiments are done quantitatively and 

 the digestion allowed to proceed for a considerable time, the increase in 

 the formol titration is practically equal to the decrease in the ids 



as determined by the Giinsberg reagent. 



The rate of peptic digestion is usually estimated by the law of Schutz 

 and Borissow, according to which the amounl of coagulated albumin 

 thai is digested in a .Melt's tube is proportional to the square n the 



amounl of pepsin. J 



The pepsin which leaves the stomach in the chyme is nol all destroyed 

 in the intestine, as was at one time believed to be the we 



have seen above, some pepsin can be d< I in tin- gastrointestinal con- 



tents. A pari of the pepsin may he absorbed into the blood and carried 

 back to the gastric glands to he used again. This would account for the 



presence of antipepsin in the blood, and also for the pr< pepsin 



in the urine. It is probable, however, that most of the pepsin 



Stroved after it enters the intestine. 



'In l!; 

 lli.il a hi| 

 titration with .1" 



tThe amounl 



, P. W.: / 



