THE ACETIC ACID BACTERIA 19 



measure to acetoin, in A. suhoxydans pyruvate is first de- 

 carboxylated to acetaldehyde and the latter compound is 

 then oxidized to acetate. A. suboxydans is thus one of a 

 very few with a yeast-type decarboxylation (also shared by 

 higher plants); it is probably associated with the failure 

 of the organism to form acetyl phosphate or acetyl CoA 

 in this organism (see below). 



Pyruvic carboxylase has been prepared from this organ- 

 ism, in a high state of purity (turnover = 300 moles COo 

 produced/minute/1 00,000 g. of enzyme). Thiamin pyro- 

 phosphate and a divalent ion serve as cofactors. Such prep- 

 arations show a higher degree of specificity than does yeast 

 carboxylase, since the bacterial enzyme responds only to 

 a-ketobutyrate, oxalacetate, and pyruvate, as shown in 

 Table 1.7. 



Acetaldehyde, The oxidation of acetaldehyde may pro- 

 ceed, as do several other oxidations in A. suhoxydans, by 

 two routes: one with TPN as coenzyme (more active), the 

 other with DPN, although it has not been possible to de- 

 termine with certainty whether two apoenzymes are pres- 

 ent (35). The specific activity of the purest preparations 

 [about 140 spectrophotometric "units" (Table 1.2)] is con- 

 siderably higher than any reported for yeast or liver. 



Acetoin, Acetoin formation (38), as depicted in Fig. 1.4, 

 has revealed that this metabolite appears to arise differently 

 from pyruvate, acetolactate, or from acetaldehyde. We 

 believe that two acetoin-forming enzymes may be present: 

 one that employs acetolactate as the preferred substrate, 

 and the other which employs acetaldehyde. A final decision 

 on this point will probably have to await further fractiona- 

 tion of the partially purified enzymes. 



Acetate, The utilization, or rather non-utilization of 

 acetate by A. suhoxydans has received much study. In ad- 



