28 



II. BIOSYNTHESIS 



demonstration of the concentration of acetyl-CoA in yeast juice.^"'^" 

 Acetyl-CoA results as the acetyl-donor from several systems, and it be- 

 haves as a substrate common to the several different acetyl-acceptor sys- 

 tems. Thus, the acetate-CoA-ATP system, the acetylphosphate-CoA- 

 phosphotransacetylase system, and the citric acid-CoA-condensing system 



ACETYL 

 PHOSPHATE 



+ CoA 



+ CoA 



ACETATE 



J CITRIC 

 1 ACID 



ACETYL- 

 SULFANILAMIDE 

 ACETYLCHOLINB 

 ACBTYLGLYCINB 

 ETC. 



Fig. 2. Donor and acceptor systems involving acetyl-CoA. Other donors include 

 acctaldehyde, pyruvate, and acetoacetate.^^ 



ACETYL -0 



CJVSH 



GAS-COCH, 



ACETYL -A. 



AClTYl DONOR 



ACfTYl-TRANSrftUNG 



Acnn AcccproB 



Fig. 3. Scheme of acetyl transfer as pictured by Lynen and co-workers.*''*" 



all serve as donors for the acetyl group. Sulfanilamide, choline, glycine, 

 and related compounds, oxaloacetate and phosphate can all serve as acetyl- 

 acceptors. Apparently, these several acetyl-acceptor systems may be re- 

 garded as competing with each other. When several of them are simul- 

 taneously present, the one which exercises the highest priority will receive 

 the acetyl groups. When an aromatic amine is present, the acetyl is used 

 to acetylate it, and a decrease occurs in the acetoacetate production.*"^ 

 According to Lynen, '*" in the transfer of acetyl groups from the donor to 

 the acceptor systems, in the presence of highly specific enzymes, the prin- 

 ciple is exactly the same as that of phosphate and hydrogen transport, i.e., 

 the bond energy is preserved when acetyl passes from the donor to the sulf- 

 hydryl group of CoA. 



i"' G. D. NoveUi, Phosphorus Metabolism, 1, 271-275 (1951). 



