The integration and control of animal acylglycerol metabolism

The major function of triacylglycerols in animals is as a source of fatty acids to be used as metabolic fuel. Any discussion about the integration of their metabolism is therefore a description of the regulation of fuel economy in the body and the transport of fatty acids between tissues involved in the synthesis, storage and oxidation of fatty acids and their glycerol esters. 

1 Fuel economy because of the essentiallity of maintaining constant blood glucose concentrations, the interconversion of different types of fuels has to be hormonally regulated 

2 The control of acylglycerol biosynthesis although the need for metabolic fuels is important, other requirements for lipids, such as membrane formation, may take precedence, requiring close integration of storage and structural lipid formation 

In animals, net triacylglycerol synthesis occurs when energy demands exceed immediate requirements. Most diets contain both fat and carbohydrates, but when there is a preponderance of energy as carbohydrates, the tissues convert them into fatty acids which are then esterified into acylglycerols. When there is a preponderance of fat in the diet, fat synthesis from carbohydrate is depressed in the tissues. The products of fat digestion are then converted into lipoproteins (section 5.3) which circulate in the bloodstream. When the lipoproteins reach the tissues, fatty acids are released from the acylglycerols at the endothelial surfaces of cells, a process catalysed by the enzyme lipoprotein lipase, and are taken up into the cells 

This phenomenon is a recently discovered form of metabolic control and enzymes that exist in different locations in the cell and can regulate metabolism by moving from one location to another are called ambiquitous enzymes. Another example in lipid metabolism is the CTP phosphoryl-choline cytidylyl transferase which regulates the biosynthesis of phosphatidylcholine (7.1.4). The diacylglycerols formed by the action of PAP 

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