August 15, 1919] 



SCIENCE 



153 



similarly. This led liim to the conclusion 

 that a close chemical relationship exists be- 

 tween the enzyme and the substance on 

 which it acts — a view which led to his fa- 

 mous analogy of the lock and key relation- 

 ship. Just as one key fits one lock, so any 

 one enzyme will act on only a certain type 

 of substance. 



In the winter of 1894 Fischer resumed 

 his earlier work on uric acid and caffeine. 

 After three years he succeeded in synthet- 

 ically producing every constituent of the 

 group, and traced them all to a mother sub- 

 stance to which he gave the name of purin 

 (a word suggested by the phrase purum 

 uricum). 



The chemist, the physiologist and the 

 pathologist can but wonder at such genius. 

 Here are the most complex and the most 

 important class of protein bodies, the so- 

 called nucleoproteins, which, as their name 

 implies, are found in the nucleus of the cell, 

 and which, in the course of their decompo- 

 sition in the body, give rise to xanthine, hy- 

 poxanthine, adanine, guanine, e<c.— all 

 typical purines. Here are these purines 

 which, in their further travels in the body, 

 come to the liver, where a larger percent- 

 age of them are oxidized to uric acid — 

 another member of the -purine family. This 

 same uric acid is a never-failmg constituent 

 of the urine, and its quantity gives valuable 

 data regarding nucleoprotein metabolism in 

 the body. This becomes of paramount im- 

 portance in such a disease as gout. The 

 inter-relationship of these complex purines, 

 as well as their relationship to plant 

 analogues, such as caffeine and theobro- 

 mine, have been as thoroughly probed by 

 Fischer as the composition of water or that 

 of air. He has gone even further. Hav- 

 ing found relationships, and having traced 

 the substances to one mother substance, he 

 has succeeded in building them all up from 

 this mother substance — a piece of work 



which with but one exception, has no equal 

 in synthetic chemistry. 



The one exception is Fischer's crowning 

 series of researches on the proteins. No 

 work approaching this had ever been done 

 before. 



Fischer was not the first to tackle this 

 problem of problems, but he was the first to 

 give the lead in the right direction. 



The crude physical methods of classify- 

 ing proteins have pointed to the fact that 

 there are some forty to fifty in number. 

 All of these, when hydrolyzed, give a large 

 percentage of the nineteen amino-aeids 

 wHch are common to most proteins; the 

 differences among proteins is most marked 

 in the amount of the various amino-acids 

 which they yield when hydrolyzed. 



Due in no small part to the labors of 

 Fischer and his co-workers most of these 

 nineteen amino acids have been synthesized 

 from simpler bodies. 



If the hydrolysis of proteins, and the 

 careful investigation of the decomposition 

 products so produced was a difficult task, 

 what are we to say of the reverse process, 

 whereby, by starting with amino-acids, we 

 build up proteins? Yet that is what 

 Fischer did. He succeeded in working 

 out methods hj which amino-aeids could 

 be chemically joined on to one another in 

 some such way as the links of a chain. 

 He has given the name polypeptids to such 

 combinations of amino-acids. 



In his most celebrated experiment in the 

 synthesis of proteins, Fischer succeeded in 

 combining eighteen amino-acids — an octa- 

 decapeptide — which is the most compli- 

 cated artificial substance that has ever 

 been produced, ajid which shows some very 

 striking resemblances to the natural pro- 

 teins, not the least of which is the way 

 trypsin, the pancreatic enzyme, breaks it 

 up into the amino-aeids out of which the 

 artificial protein was built. 



