Biologically Important Substances Related to Nucleotides

As defined, the nucleotides are AT-glycosylpurines or -pyrimidines esteri-fied with phosphoric acid (A-base-sugar-phosphoric acid). Several vitamins of the B group and coenzymes have closely similar structures with different aglycons, with ribitol instead of ribose, or with a different sugar esterifying the end of the phosphate chain. The function of some of these compounds is discussed in Chapter XIII. 

Coenzyme /. A heat-stable, dialyzable substance occurs in yeast and muscle tissue which is essential for the in vitro fermentation of sugars by yeast extract. Concurrent work in the laboratories of Warburg, Christian, and Griese, and Euler and Schlenk (137) established the following formula for coenzyme I (also known as cozymase, codehydrogenase I, or diphospho-pyridine nucleotide (DPN)  

Coenzyme I might be considered as a mixed dinucleotide consisting of adenylic acid and a second nucleotide compound which has one of the B-complex vitamins (nicotinamide) as the nitrogen base. Almond emulsin hydrolyzes coenzyme I and iV -ribosylnicotinamide may be separated from the hydrolyzate 138), 

Coenzyme III. A third thermostable, dialyzable factor, coenzyme III, capable of replacing DPN in a number of dehydrogenases, has been iso- 

von Euler and F. Schlenk, Z. physiol. Chem. 246, 64 (1937) F. Schlenk, B. Hogberg, and S. Tingstam, Arkiv Kemi Mineral. Geol. A13, 11 (1939). 

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