TCA cycle = beta oxidation?

Morgan J Ryan -- Neil Patterson Publishers morgan at
Tue Nov 2 21:57:01 EST 1993

	Hi. Your ingenuity please.
	Three sequential reactions of fatty acid oxidation are chemically
identical to three reactions of the citric acid cycle. What is the
explanation for this textbook chestnut? Is there some chemical or
structural biological logic?
	The reactions are fatty acyl CoA to 3-ketoacyl CoA and succinate
to oxaloacetate. Basically that's:
	beta oxidation		   	citric acid cyc
R--CH2--CH2--C(O)--COA ->	COO--CH2--CH2--COO 
R--CH==CH--C(O)--CoA ->		COO--CH==CH--COO
R--CHOH--CH2--C(O)--CoA -> 	COO--CHOH--CH2--COO
R--C(O)--CH2--C(O)--CoA		COO--C(O)--CH2--CO
	I've heard some pretty impressive biochemists mock each other's
ideas about why this sequence is repeated. Is there some subterranean
chemical logic? I don't know if there is any structural congruity among
the enzymes of the parallel reactions.Worth a look, I suppose, if there
isn't a more obvious explanation.
 Morgan Ryan / morgan at

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