Fatty adds hormone-sensitive lipase

The mobilization of stored fat requires the hydrolytic release of fatty adds and glycerol from their TAG form. This process is initiated by hormone-sensitive lipase, which removes a fatty acid from carbon 1 and/or carbon 3 of the TAG. Additional lipases specific for diacylglyc-erol or monoacylglycerol remove the remaining fatty acids. 

Figure 5.5 Hormone-induced fatty add mobilisation in adipocytes. Through hormone-induced rises in intracellular cAMP levels, phosphorylation (activation) of hormone-sensitive lipase initiates the mobilisation of fatty acids from triacylglycerol.

The hydrolysis of TGs to FFAs and glycerol is catalyzed by a lipase in adipocytes called hormone-sensitive lipase. This enzyme catalyzes the hydrolysis of fat deposits in adipose tissue or wherever adipocytes arc found. The rate of liberation of fatty adds and of the byproduct glycerol from the adipose tissue may be greater than the rate at which they can be oxidized by other tissues. Under these conditions, the concentrations of FFAs and glycerol increase in the plasma. The data in Table 4.9 are from a study of human subjects who exercised on a stationaiy bicycle. Blood samples withdrawn during rest and at the indicated times during exercise show that FFA concentrations increased from 0 43 mM at rest to nearly 2.0 mM after 3 hours of work. 

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