Elementary steps in the reaction mechanism of chicken liver fatty acid synthase: .beta.-ketoacyl reductase and enoyl reductase

Biochemistry ◽  
1985 ◽  
Vol 24 (2) ◽  
pp. 290-297 ◽  
Author(s):  
Jean A. H. Cognet ◽  
Gordon G. Hammes
Keyword(s):  
Fatty Acid ◽  
Reaction Mechanism ◽  
Fatty Acid Synthase ◽  
Chicken Liver ◽  
Liver Fatty Acid ◽  
Enoyl Reductase ◽  
Elementary Steps

scholarly journals Inhibition of the condensing component of chicken liver fatty acid synthase by iodoacetamide and 5,5′-dithiobis-(2-nitrobenzoic acid)

1983 ◽  
Vol 215 (3) ◽  
pp. 545-553 ◽  
Author(s):  
E Varagiannis ◽  
S Kumar
Keyword(s):  
Fatty Acid ◽  
Fatty Acid Synthesis ◽  
Fatty Acid Synthase ◽  
Condensation Reaction ◽  
Acid Synthesis ◽  
Chicken Liver ◽  
Liver Fatty Acid ◽  
Nitrobenzoic Acid ◽  
Proposed Model ◽  
Cross Links

Chicken liver fatty acid synthase is inhibited by the thiol-modifying reagents 5,5′-dithiobis-(2-nitrobenzoic acid) and iodoacetamide. Total inactivation of the activity for fatty acid synthesis requires the modification of about 8 of the nearly 50 freely accessible thiol groups per molecule. The differential binding of iodo[14C]acetamide to phenylmethylsulphonyl fluoride-modified enzyme in the absence and in the presence of excess acetyl-CoA shows complete modification of one cysteine-SH site of the condensing enzyme and partial modification of the pantetheine-SH site for a total of approx. 1.4 mol of iodoacetamide bound per mol of enzyme. The reaction of the enzyme with 5,5′-dithiobis-(2-nitrobenzoic acid) generates disulphide cross-links for each molecule of the reagent added, but 95% of these cross-links are intrasubunit. Both the iodoacetamide- and 5,5′-dithiobis-(2-nitrobenzoic acid)-modified species catalyse all the component partial reactions of fatty acid synthesis except the condensation reaction. The results obtained with iodoacetamide show that in the dimeric fatty acid synthase modification of one cysteine-SH condensing site and/or one pantetheine-SH site per dimer is sufficient to affect inhibition of condensing activity and the activity for fatty acid synthesis, and are in accord with a recently proposed model for the mechanism of action of animal fatty acid synthases [Kumar (1982) J. Theor. Biol. 95, 263-283].

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