244 



SCIENCE 



[N. S. Vol. XXVII. No. 685 



case of protein. Gelatin, which resembles 

 albumin in its superficial reactions and 

 which contains approximately the same 

 amount of nitrogen, is, as we know, quite 

 incapable of taking the place of albumin 

 in supplying the needs of the body for 

 protein food. Yet, gelatin yields on de- 

 composition many of the disintegration 

 products furnished by albumin. Still, 

 there are differences in the character and 

 proportion of the cleavage products which, 

 while not sufficiently marked to modify the 

 ordinary protein color reactions, etc., are 

 enough to indicate a difference in chemical 

 structure, and owing to this difference in 

 structure gelatin is quite unable to repair 

 the waste of tissue in body metabolism. 

 To every one at all familiar with protein 

 chemistry the recent advances in knowledge 

 of the hydrolytic cleavage products of this 

 class of substances are more or less known. 

 All proteins by appropriate methods of 

 disintegration break down into a number 

 of monoamino and diamine acids. Thirty 

 years ago these hydrolytic cleavage 

 products were represented mainly by 

 leucine, tyrosine, aspartic and glutaminic 

 acid; but now, as a result of efforts in 

 many quarters, the number of such de- 

 composition products has risen to at least 

 seventeen. The significance of this state- 

 ment is apparent when we remember that 

 these cleavage products represent the 

 building stones which make up the finished 

 structure of the protein molecule, and if 

 the time ever comes when we know all of 

 these building stones, we shall then without 

 doubt be able to construct or synthesize 

 this most important substance. 



Some of the most careful and painstak- 

 ing work on the hydrolysis of proteins has 

 been done in our own country by Dr. 

 Thomas B. Osborne and his co-workers at 

 New Haven. Examination of the results 

 reported reveals several very important 

 facts. Take, for example, some of the 



latest data afforded as in the hydrolysis of 

 phaseolin,^ the globulin of the kidney bean, 

 formerly called legumin. Here, sixteen 

 different cleavage products were identified 

 and determined. The method of hydrol- 

 ysis and the methods of separating the 

 different amino acids were carried out by 

 persons skilled by long practise and under 

 the best of conditions, yet the percentage 

 of total cleavage products determined 

 amounted to only 54.27. Again, in the 

 hydrolysis of excelsin,^ the characteristic 

 globulin of the Brazil-nut, the total yield 

 of cleavage products was 61.09 per cent. 

 Finally, in the hydrolysis of hordein,'' the 

 alcohol-soluble protein of barley, 71.32 

 per cent, of cleavage products was sepa- J| 

 rated. In other words, by the best ^ 

 methods available and in the hands of 

 skilled workers trained to take advantage 

 of all the knowledge available, chemists are 

 able at present to separate and identify 

 only 54 to 71 per cent, of the total yield 

 of cleavage products which results from 

 the hydrolysis of protein. This un- 

 doubtedly means that there are still some 

 building stones in the protein molecule 

 with which as yet we are unfamiliar. 



It needs no argument to convince any 

 one that here lies a most important field of 

 work; here is a problem the solution of ,^ 

 which gives promise of rich rcAvard, both to ^a 

 the chemist and to the physiologist. Of 

 course, it is possible that the seventeen 

 cleavage products referred to represent all 

 the different types that are formed by 

 hydrolysis and that the apparent deficiency 

 is due simply to inadequate methods of 

 separation. This, however, is not very 

 probable, and it is to be noted in this con- 

 nection that the results reported by Abder- 

 halden and his co-workers in Germany are 



' American Journal of Physiology, Vol. XVIII., 

 p. 295, 1907. 



'Ihid., Vol. XIX., p. 53, 1907. 

 'Ibid., Vol. XIX., p. 117, 1907. 



