Fatty acids, binding protein transport, carnitine

Fatty acids are more efficiently degraded because of increased synthesis of molecules that facilitate fatty acid transport and oxidation. The concentration of citric acid cycle and (3-oxidation enzymes increases, as well as the components of the ETC. In addition, the capacity of the muscle cell to remove fatty acids from blood and to transport them into mitochondria increases. For example, increases in the synthesis of fatty acid transporter proteins and fatty acid-binding proteins, as well as carnitine and carnitine acyltransferase, have been observed. 

Fig. 23.1. Overview of mitochondrial long-chain fatty acid metabolism. (1) Fatty acid binding proteins (FaBP) transport fatty acids across the plasma membrane and bind them in the cytosol. (2) Fatty acyl CoA synthetase activates fatty acids to fatly acyl CoAs. (3) Carnitine transports the activated fatty acyl group into mitochondria. (4) p-oxidation generates NADH, FAD(2H), and acetyl CoA (5) In the liver, acetyl CoA is converted to ketone bodies...

Within the liver, they bind to fatty acid-binding proteins and are then activated on the outer mitochondrial membrane, the peroxisomal membrane, and the smooth endoplasmic reticulum by fatty acyl CoA synthetases. The fatty acyl group is transferred from CoA to carnitine for transport through the inner mitochondrial membrane, where it is reconverted back into fatty acyl CoA and oxidized to acetyl CoA in the (3-oxidation spiral (see Chapter 23). 

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