46 BACTERIAL FERMENTATIONS 



or just thiolase for short, was later purified from animal 

 sources and studied extensively. 46 - 47,48 Several other enzymes 

 catalyzing specific reactions in the reversible conversion of 

 acetoacetyl-SCoA to butyryl-SCoA have also been purified 

 from animal tissues during the last few years. 46 ' 49 - 50,51,52 



Current Knowledge of the Path of Butyrate Synthesis 

 in Bacteria. The accumulated information obtained with 

 animal and bacterial enzyme systems indicates that butyr- 

 ate formation in CI. kluyveri involves the reactions shown 

 in Fig. 2. Reactions I, II, and III have already been dis- 



±HSCoA 

 r>2CH 3 COSCoA ^ CH3COCH2COSC0A 



2CH3CHO CH3CHOHCH2COSCOA 



il T2H Vl ±H 2 



2CH3CH2OH CH 3 CH=CHCOSCoA 



V1 1 ±2H 



vii Ik 



LM2H3COSC0A+CH3CH2CH2COOH z^±r CH3CH2CH2COSC0A 



+CH3COOH 



Fig. 2. Butyric Acid Synthesis in Clostridium kluyveri. 



cussed; reaction IV is the reduction of acetoacetyl-SCoA to 

 /?-hydroxybutyryl-SCoA catalyzed by the enzyme /?-hydroxy- 

 butyryl-SCoA dehydrogenase; reaction V is the dehydration 

 of yg-hydroxybutyryl-SCoA to crotonyl-SCoA catalyzed by 

 the enzyme crotonase; reaction VI is the reduction of cro- 

 tonyl-SCoA to butyryl-SCoA by the enzyme butyryl-SCoA 

 dehydrogenase; and reaction VII is the transfer of the SCoA 

 group from butyrate to acetate catalyzed by the fatty acid 

 SCoA-transphorase. 



Some evidence for the occurrence of these reactions in 

 CI. kluyveri, in addition to that already discussed, has 

 accumulated. The oxidation of butyryl-SCoA to aceto- 



