NUCLEOTIDES AND COENZYMES 



adenylic deaminase, or FMN by its action as a coenzyme for 

 yeast TPN-cytochrome c reductase. Assays of this sort are 

 sensitive, rec^uire minute amounts of material, and are highly 

 specific, so that they may be performed even in the presence of 

 impurities. 



Once a coenzyme has been isolated, and its structure deter- 

 mined, a number of ancillary facts about its chemistry begin to 

 accumulate. Necessary documentation for the proper under- 

 standing of coenzyme function is provided by physical data such 

 as: (7) absorption spectra, at various jfcH values; (2) pK. values 

 obtained by classical titrimetric methods or by the recently 

 introduced electrophoretic mobility technique of Bock and 

 Alberty (7) ; (3) crystal structure, bond angles and distances 

 (i.e., the exact three-dimensional shape of the molecule) as 

 revealed by x-ray diffraction patterns; (4) oxidation potentials 

 of appropriate groups, (5) free energies of hydrolysis of phos- 

 phate groups; (6) chemical studies such as the behavior and 

 interaction of reactive groupings, and (7) the comparative study 

 of appropriate model compounds. Too often such data have been 

 sorely needed but unavailable, and enzymology is indebted to 

 Meyerhof, Michaelis, R. Kuhn, and Borsook, to name only a 

 few, who have enriched the literature with accurate information 

 in the above categories. A singularly outstanding effort along 

 the above lines has been the complete and extensive docu- 

 mentation of the properties of vitamin B12, as described by Lester 

 Smith and his group (14) and by Folkers (15). 



Concerning the dynamic state of coenzymes in tissues, 

 there has accumulated considerable evidence on the enzymatic 

 breakdown and synthesis of these substances. As with most 

 other classes of metabolites, knowledge of the former phase has 

 preceded the latter. We know of pyrophosphatases which 

 split the dinucleotides, of nucleotidases, i.e., phosphatases, 

 which are selective for the various isomeric positions of the 

 •phosphate group, and nucleosidases which cleave the A^- 

 glycoside bonds. Other enzymes, which degrade the ring and 

 sugar moieties, are well known but outside the purview of the 



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