IV. BIOCHEMICAL SYSTEMS 481 



Nicotinamide containing coenzymes have significance not onlj^ in verte- 

 brate biochemistry but in the vegetable kingdom as well. This became clear 

 quite earl}^ not onlj' from the studies on yeast fermentation^ but especially 

 due to the studies of the Lwoffs with factor V, an essential growth factor 

 for Hemophilus parainfluenzal They established the identity of factor \ 

 with the nicotinamide coenzymes and discovered that these substances 

 functioned biochemicall}" in these microorganisms much as had already 

 been found in enzyme systems derived from mammalian sources (also see 

 p. 550). 



B. COENZYMES CONTAINING NICOTINIC ACID 



Two, and only two, coenzymes are known to contain nicotinic acid.^'' 

 These have been described inider various names in the literature. 



1. Coenzyme I, codehydrogenase I, cozymase, Harden's coferment, core- 

 ductase, factor V, codehydrase I, and diphosphopyridine nucleotide. 



2. Coenzyme II, codehydrogenase II, Warburg's coferment, codehydrase 

 II, and triphosphopyridine nucleotide. 



Since names which depict chemical structure are generally less confusing, 

 the terminology of diphosphopyridine nucleotide (DPNHo for the reduced 

 form) and triphosphopyridine nucleotide (TPN and TPNH2) will be used 

 in this chapter to refer to coenzymes I and II, respectively. It is recognized 

 that this terminology is not quite correct chemically, since the term nucleo- 

 tide itself implies phosphoric acid content. Nevertheless this terminology 

 seems preferable by virtue of common usage and in view of the fact that 

 these were the names originally suggested by Warburg and Christian. 



C. ISOLATION AND IDENTIFICATION 



1. TPN was the third coenzyme to be discovered and the first found to 

 contain nicotinamide as part of its structure. In 1934 Warburg and Chris- 

 tian^ isolated a nitrogen-containing base from their "Co-ferment" (TPN) 

 which was quickly identified as nicotinamide.- These and later studies^' ^ 

 showed that their coenzyme contained 1 molecule each of adenine and 

 nicotinamide, 3 molecules of phosphoric acid, and 2 molecules of pentose. 

 However, there was some uncertainty that one of the sugar molecules 



6 A. LwofT and M. Lwoff, Proc. Roy. Soc. (London) B122, 352, 360 (1937). 



"" A probable exception to this has been recorded recently by T. P. Singer and E. 

 B. Kearney [Abstr. 2nd Intern. Congr. Biochem. Paris p. 307 (1952)], who discovered 

 a pyridine nucleotide, which was not identical with any known coenzyme, in 

 Proteus vulgaris. This coenzyme was necessary for the o.Kidation of cysteinesulfinic 

 acid to cysteic acid and for the dehydrogenation of /3-sulfinylacetic acid. The 

 structure of this pyridine nucleotide is not yet known. 



' O. Warburg, W. CJiristian, and W. Griese, Biochem. Z. 282, 157 (1935). 



