Section K - Lipid metabolism

Structure and Fatty acids have a long hydrocarbon chain with a terminal carboxylic acid 

Nomenclature Fatty acids are named according to the number of carbon atoms in the chain and the number and position of any double bonds. Some of the more common fatty acids are palmitate (06 0), stearate (08 0), oleate (08 1), linoleate (08 2), linolenate (08 3) and arachidonate (C20 4). The double bonds in a fatty acid are usually in the cis configuration. 

Roles Fatty acids have four major biological roles 1. They are components of membranes (glycerophospholipids and sphingo- lipids) 2. Several proteins are covalently modified by fatty acids 3. They act as energy stores (triacylglycerols) and fuel molecules 4. Fatty acid derivatives serve as hormones and intracellular second messengers. 

Prostaglandins Prostaglandins and the other eicosanoids (prostacyclins, thromboxanes and leukotrienes) are derived from arachidonate. These compounds all act as local hormones. Aspirin reduces inflammation by inhibiting prostaglandin synthase, the enzyme that catalyzes the first step in prostaglandin synthesis. 

Related topics Membrane lipids (El) Triacylglycerols (K4) Fatty acid breakdown (K2) Cholesterol (K5) Fatty acid synthesis (K3) 

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Ethylene is rather inert, but it is metabolized slowly, some of it to ethylene glycol.326 Plants store N-malonyl-ACC as a metabolically inert pool. Excess ACC can be deaminated in a PLP-dependent reaction to 2-oxobutyrate (step k, Fig. 24-16), a process that also occurs in bacteria able to subsist on ACC.327/327a There may also be other mechanisms for ethylene formation, e.g., peroxidation of lipids during scenescence of leaves.328 See also Chapter 31, Section G. 

The protein moieties of lipoproteins fulfil two main functions firstly, they provide a means of solubilizing the lipid particles and maintaining their structural integrity (section 5.3.5(k)). Secondly, they are important in identifying the lipoprotein and directing its metabolism in specific ways. The main metabolic functions of the apolipoproteins are shown in Table 5.11. The term apoprotein was first used in 1963 to describe the protein moiety of a number of delipidated lipid—protein complexes and the more specific term apolipoprotein will be used here. It has now become accepted to use a series of letters A-E to identify apolipoproteins but it soon became apparent that most of these could be divided further into several sub-classes (Table 5.11). These are usually referred to in abbreviated form, thus apoAi, apoCs, etc. 

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