FRANK M. HUENNEKENS 



Structure oj Coenzymes 



One may pause at this point and inquire how we have 

 reached our present state of knowledge that enables us to as- 

 semble the information in Table I. When a coenzyme has 

 been established definitely as part of an enzymatic process by the 

 criteria mentioned above, there ensues the fascinating game of 

 isolating, if possible in pure form, and of characterizing the 

 coenzyme in question. On occasion the game is played in a 

 spirit of intense rivalry between competing groups. One might 

 also remark parenthetically that of late the pace of the game has 

 been stepped up — as witnessed, for example, by the relatively 

 short time that elapsed between the postulation of lipoic acid as 

 a coenzyme of pyruvic oxidase and its isolation, characterization, 

 and total synthesis. 



In part, this acceleration is due to the introduction of revo- 

 lutionary new methods. In the past, the isolation of a co- 

 enzyme was accomplished principally by means of precipitation 

 as heavy metal salts, precipitation by organic solvents, or ex- 

 traction into organic solvents. These methods were somewhat 

 nonspecific, so that impurities were only slowly removed over 

 many steps with the resultant loss in yield. Now, these methods 

 have not been abandoned and still find a useful place in puri- 

 fication schemes, but the emphasis has shifted toward newer 

 techniques, based mainly upon principles of chromatography. 

 Contemporary workers in the field are presented with a glittering 

 array of new tools: ion-exchange chromatography, adsorption 

 chromatography, partition chromatography, including counter- 

 current distribution, and even large-scale paper chromatography. 

 The success of the chromatographic method lies in the fact that 

 it induces a change of phase, in turn, of each component in a 

 mixture. Thus, the components are spread out for display, as 

 it were, before the eyes of the investigator. For example, the 

 basic technique introduced by Cohn and Carter (12), i.e., 

 separation of nucleotides on Dowex-1 ion-exchange resins, has 

 been modified by Potter and his colleagues (23) so that the 

 composition of the eluting medium is constantly changing 



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