2 METABOLIC PATHWAYS IN MICROORGANISMS 



as well as several others. The organism was at first regarded 

 as a most versatile one, being adaptable to so many sub- 

 strates; but, it may be more nearly correct to consider it as 

 a metabolic "cripple," not particularly better able to attack 

 substrates than many other organisms, and unable to oxi- 

 dize these beyond the first one or two steps. Perhaps the 

 chief reason for this is the fact, which will be discussed 

 later, that the organism has no Krebs cycle, and thus lacks 

 the "prairie fire" of terminal oxidation that most other 

 organisms, whether men or mice, enjoy. 



Our interest in this organism began, however, not with 

 the oxidations that it carried out, but with finding a 

 reason for its unusual pantothenic acid requirement. An 

 earlier lecturer in this series, Dr. Frank M. Strong (3), has 

 described much of the literature dealing with coenzyme A, 

 so I will dwell on it only for a moment. Suffice it to say 

 here that this organism is ten to twenty times as sensitive 

 to bound forms of pantothenic acid [coenzyme A, pante- 

 theine {L. bulgaricus factor, LBF), pantothenyl cysteine] as 

 it is to the free vitamin (4). This fact was discovered in 

 our laboratory, where it gave rise to the description of a 

 pantothenic acid conjugate which we abbreviated PAC 

 (5). This conjugate was not fully characterized, but it is 

 now regarded as a fragment of the coenzyme A molecule. 

 The enhanced activity of conjugates of pantothenic acid 

 toward A. suhoxydans has been of aid to various investiga- 

 tors in their studies of derivatives of pantoic acid that lead 

 to coenzyme A (3, 6, 7). 



The observed superiority of coenzyme A over the free 

 vitamin as a growth promoting agent, may be rationalized 

 by the fact that cells grown deficient in pantothenate (and 

 hence coenzyme A) have a lower lipid content than normal 



