CHjOH 



CHOH 



CH^OPO^ 



CC-D-GLYCEROL 

 PHOSPHATE 



CH. 





 ,3(CH,^4-C0A 



9=0 



(9H0H)n 

 CH^OPO^ 



HOPO^ 



-CfeC-CHg-C-CoA. 

 MALONYL COA 



CHj-C-CHg-C-Coft 

 ACETOACETYL CoA 



OH 

 CHj-C-CHg-C-CoA 



^\ 4[H] 



MEVALONATE 

 OH 



CH3-9-cH2-ay)H 



CH2 



/ \ 



SJERODS CAfiOTENaDS 



Figure 7. Pathways from carbon reduction cycle to acetyl phos- 

 phate and glycolic acid. For details of the carbon reduction cycle, 

 see Figure 2. 



of the thiazole ring does exchange rapidly in D2O (49). In 

 support of an analogous mechanism for the role of ThPP 

 in the oxidation of pyruvate, Krampitz and co-workers (51, 

 52) synthesized the postulated intermediate, an acetaldehyde- 

 ThPP compound with the acetaldehyde bonded to the num- 

 ber 2 carbon atom of the thiazole ring as an alpha hydroxy- 

 ethyl group. This compound was found to be active in the 

 reactivation of carboxylase and also to be capable of non- 

 enzymatic reaction with acetaldehyde to give acetoin. The 

 postulated mechanism for the oxidation of pyruvic acid thus 

 begins with a reaction between pyruvate and ThPP to give 

 addition of the carbonyl carbon to the thiazole-ring-position 

 number 2. Concurrently or immediately following this addi- 



42 



