PREFACE 



adenine dinucleotide and vasopressin to mention but two out- 

 standing examples. 



Methodology was not the principal limiting factor in all 

 structural problems. The solution of the problem of the 

 molecular architecture and stereochemistry underlying protein 

 structure required new ideas and concepts as well as more 

 powerful tools for analysis. The helix principle which has 

 been shown to apply successfully to a variety of proteins and to 

 nucleic acid has provided one of the keys for deciphering the 

 hitherto unintelligible x-ray diagrams of a variety of macro- 

 molecules. 



A direct consequence of the advances in methodology was 

 the growth of enzyme chemistry from a toddler to a giant 

 dominating the whole of biochemistry. During the past ten 

 years practically all the enzymatic and chemical details of the 

 citric, pentose, fatty acid, and urea cycles have been elucidated. 

 The enzymatic synthesis of nucleic acid, lecithin, cephalin, 

 fatty acids, sucrose, lactose, purines, pyrimidines, and dinucleo- 

 tides has been accomplished by means of isolated enzymes or cell- 

 free enzyme systems. The chemical details of the reactions 

 which intervene in the enzymatic synthesis of hemin and cho- 

 lesterol are now almost fully documented. Hundreds of enzymes 

 which implement not only the above sequences but many 

 others too numerous to be listed have been isolated, character- 

 ized, and studied in detail. Indeed few of the classical problems 

 of metabolism remain unsolved or are not already close to 

 solution. 



The list of coenzymes has more than doubled during the 

 past ten years. Lipoic acid, coenzyme A, uridine diphospho- 

 glucose, uridine diphosphogalactose, uridine diphosphoglucu- 

 ronic acid, glucose- 1,6-diphosphate, 1,3-diphosphoglyceric acid, 

 guanosine diphosphate, molybdenum, and cytosine diphospho- 

 choline are some of the more prominent recent additions to the 

 roster of known cofactors. 



The era of each investigator preparing his own cofactors, 

 special chemicals, and even enzymes is now all but over. A 



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