BacferJal Mefabollsm 81 



coenzyme A substrate compounds have been found to be 

 essential in other reactions catalyzed by bacteria. For ex- 

 ample, Whitely (28) has shown that succinyl CoA and pro- 

 pionyl CoA are involved in the formation of propionate 

 by the propionic acid bacteria, and Hayaishi (9) has found 

 that malonyl CoA is an intermediate in the conversion of 

 malonate to acetate by Pseudomonas, 



Though our knowledge of the enzymatic reactions in- 

 volved in butyrate synthesis is fairly detailed, it must be 

 admitted that our understanding of the role of this process 

 in the metabolism of C. kluyveri is still very deficient. We 

 do not know, for example, what benefit the organism de- 

 rives from the conversion of alcohol and acetate to buty- 

 rate, since the useful energy derived from the oxidation 

 of the alcohol appears to be consumed again in the syn- 

 thesis of butyrate, without leaving any energy available 

 for other synthetic reactions. 



Formation of Energy-Rich Compounds 



Another essential aspect of bacterial metabolism is the 

 nature of the chemical mechanisms by which energy is 

 generated and made available for synthetic purposes in 

 the cell. We owe particularly to Lipmann the idea that 

 compounds containing the so-called energy-rich phosphate 

 bond represent a common currency for energy exchange 

 in living organisms. More recently, as a result of the work 

 of Lipmann, Lynen, and others, various thioesters, like 

 acetyl CoA, also have been shown to play a prominent 

 role in energy transfer. 



The formation of such energy-rich compounds has been 

 studied extensively in animals and yeast, and it has been 

 found that they are usually formed in two ways, either by 

 the oxidation of substrate molecules such as aldehydes and 

 a-keto acids, or as a result of the transfer of electrons by 

 way of flavoproteins and the cytochrome system to oxygen. 



