lec33 - Biochemistry I Fall Term, 2004 December 8, 2004...

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1 Biochemistry I Fall Term, 2004 December 8, 2004 Lecture 33: Catabolism of Fatty Acids Assigned reading in Campbell: Chapter 18.1-18.5 Key Terms: Acyl-carnitine Acyl-CoA β -oxidation Lipases Phospholipases Ketone bodies Links : ( I ) Review Quiz on Lecture 33 concepts Formation of Acyl-CoA The fatty acids in the cytosol are coupled to Coenzyme A to form acyl-CoA. The activation reaction is catalyzed by acyl-CoA synthetase and involves the following steps (Fig. 18.4): 1. Nucleophilic attack of carboxyl group of fatty acid towards phosphate of ATP 2. Formation of an acyl-AMP intermediate with release of PP i . This reaction is slightly endergonic; however, it is driven by the subsequent hydrolysis of PP i . This is another example of: The hydrolysis of a high energy compound to make a reaction irreversible; and Irreversibility in the first step of a pathway. 3. Nucleophilic attack of the sulfur group of CoA on the carbonyl carbon of the fatty acyl- AMP intermediate. The resulting high energy thioester bond ( G = -31.5 kJ/mol for hydrolysis) preserves the high energy of the ATP used to form the acyl-CoA. Note that it is only necessary to utilize ATP in the formation of the first thioester bond.
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lec33 - Biochemistry I Fall Term, 2004 December 8, 2004...

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