Febbuaey 14, 1908] 



SCIENCE 



247 



thereby suggesting different degrees of 

 attraction or union. Thus, it has been re- 

 cently shown by Abderhalden and Voegt- 

 lin^ that in the digestion of edestin by 

 activated pancreatic juice certain of the 

 amino acids are rapidly freed from their 

 combinations, while others are liberated 

 much more slowly; tyrosine, for example, 

 was wholly free in two days' time, while 

 glutaminic acid even at the end of sixteen 

 days was split off only to the extent of 

 two thirds of the amount present in the 

 edestin molecule. The same has been 

 found true in the pancreatic digestion of 

 casein; tyrosine is rapidly and completely 

 split off, glutaminic acid, on the other 

 hand, very gradually. Thus, with casein 

 and activated pancreatic juice the full 

 amount of tyrosine contained in the pro- 

 tein was liberated in three days, while, as 

 a rule, glutaminic acid could be obtained 

 free only to the extent of 60-80 per cent, 

 of the amount present and then only after 

 three weeks of continued proteolysis. It 

 is thought, though by no means settled, 

 that alanine, valine, leucine, etc., behave 

 exactly like glutaminic acid, while phenyl- 

 alanine, proline and glyeoeoll do not admit 

 of being freed from their combinations at 

 all by the hydrolytic action of pancreatic 

 juice. In other words, we see suggested 

 here different degrees of attraction, dif- 

 ferent lines of combination among the 

 many units entering into the construction 

 of the protein molecule, which are well 

 worthy of careful consideration, since they 

 may have both chemical and physiological 

 significance. It is no exaggeration to say 

 that every additional fact bearing upon the 

 nature and combinations of the chemical 

 units present in the protein molecule 

 promises to be of the greatest help in un- 

 raveling the many complexities now con- 



' Zeitsclirift fur phi/siologischen Chemie, Band 

 XXXy., p. 315, 1907. 



fronting us in our understanding of the 

 nature of this most important substance. 



Any consideration of protein cleavage as 

 a physiological process naturally brings 

 into the foreground enzymatic action in 

 general, which is rapidly becoming recog- 

 nized as the most important method of 

 chemical change occurring in living organ- 

 isms. We need go back only a few years 

 when practically our knowledge of enzy- 

 matic action as it occurred in man and 

 the higher animals was limited to the 

 transformations of starch, protein and fat 

 by the digestive juices of the gastro-intes- 

 tinal tract, and in plants to the alteration 

 of starch through diastase. But to-day 

 what a change has come over our under- 

 standing of enzymolysis and how wide- 

 spread the varied processes now included 

 under this term ! The bio-chemical reac- 

 tions which are produced through the 

 agency of the many enzymes so widely dis- 

 tributed in nature are not only numerous, 

 but exceedingly varied in character, and we 

 are practically justified in the assumption 

 that the great majority of the intra- and 

 extra-cellular chemical changes taking- 

 place in living organisms are the result of 

 enzyme action. The old-time distinction 

 between ferment action and the so-called 

 vital action of living cells no longer carries 

 weight. As is now well known, not hydrol- 

 ysis merely, but oxidation, deamidizatiou 

 and a whole host of well-defined chemical 

 changes, such, for example, as are char- 

 acteristic of the different types of inter- 

 mediary metabolism in the higher animals, 

 are due to intra- and extra-cellular en- 

 zymes, formed, it is true, through the con- 

 structive power of living cells, but acting 

 as simple chemical or physico-chemical 

 agents and capable of producing their 

 transformations whether in contact with 

 the cells where they are formed or merely 

 dissolved in suitable extracts free from 

 tissue elements. Not only do these state- 



