78 PHYSIOLOGICAL CHEMISTRY. 



products are secured. It will be shown below that the effects 

 of prolonged tryptic digestion are very nearly the same as 

 observed with hydrochloric acid. This is a point of the 

 highest practical importance, as it gives us some insight into 

 the complex physiological process. And in peptic digestion 

 also, where very weak hydrochloric acid and pepsin are em- 

 ployed, essentially the same products result provided the time 

 of the action be made sufficiently long. 



RESULTANT CHARACTER OF THE PROTEIN MOLECULE. 



While the various decompositions detailed above give us 

 some insight into the number and kind of groups combined in 

 the protein complex, they do not, unfortunately, show us much 

 as to the manner in which these groups are combined. We 

 are not, as yet, able to picture to ourselves a large molecule in 

 which the leucine, tyrosine, aspartic acid, glycocoll, and so on, 

 are united to form a molecule with the general' properties and 

 molecular weight as large as we assign to even the simplest 

 proteins, but a step has been made in that direction through the 

 synthesis of various polypeptidcs carried out by Fischer and 

 Curtius, who have succeeded in condensing several amino acids 

 into one molecule with certain properties suggesting those of 

 the peptones. These bodies will be referred to in a later chap- 

 ter. Hofmeister has suggested the possibility of the combi- 

 nation of amino acids in large groups by the following general 

 scheme : 



NHCHCO NHCHCO NHCHCO NHCHCO 

 I I I I 



CH 2 CH 2 CH 2 (CH 2 ) 3 



CH 3 -CH-CH 3 CeH^OH COOH CH 2 NH 2 



Leucine Tyrosine Aspartic Acid Lysine 



The recognition of the various component groups suggests 

 some reasons why the proteins may exhibit acid and basic 

 behavior at the same time. Of most of these protein com- 

 pounds the basic character is the more pronounced and more 

 readily observed; that is, their acid combining power. Some 



