There is also a phospholipase A1, which is able to cleave the sn-1 ester bond. Phosphatidylarsenocholine is a minor component of the lipids of a number of marine organisms and is discussed in the web page dealing with arsenolipids. Impaired phosphatidylcholine biosynthesis has been observed in a number of pathological conditions in the liver in humans, including the development of non-alcoholic fatty liver disease, liver failure and impaired liver regeneration. Elsevier, Amsterdam - several chapters - see Science Direct. It is argued that this diffusion process is dependent on the lipophilicity and size of the fatty acid Kampf et al. There are two fatty acids for which the body cannot synthesize sufficient quantities, and must rely on dietary sources.
Each cycle of reactions produces one molecule of FADH2, one molecule of NADH, one molecule of acetyl CoA, and a fatty acyl derivative that is two carbons shorter than that in the previous step.
CPT2 then reforms the fatty acyl-CoA. Lipolysis principally occurs in the adipose tissue and is facilitated by a set of enzymes known as lipases Ahmadian et al. Studies of labeled phosphatidylcholines and phosphatidylethanolamines have shown that the uptake of these phospholipids occurs on a different timescale compared to vesicular protein cargo Vance et al. Because of the increased demand for membrane constituents, there is enhanced synthesis of phosphatidylcholine in cancer cells and solid tumours; the various biosynthetic and catabolic enzymes are seen as potential targets for the development of new therapeutic agents.
In particular, the brain takes part in a substantial amount of phospholipid synthesis Ross et al. This process occurs at the ER, but can also occur in ER-derived vesicles as well as the plasma membrane Kim et al. In such cases, cholesterol is packaged into HDLs, which return it to the liver. Impaired phosphatidylcholine biosynthesis has been observed in a number of pathological conditions in the liver in humans, including the development of non-alcoholic fatty liver disease, liver failure and impaired liver regeneration.
The carboxylation of acetyl CoA to malonyl CoA is irreversible and the rate-limiting step in fatty acid synthesis Ha and Kim, Geiger, O. Glycerolphosphate, the rate-limiting step of TAG synthesis, is converted to lysophosphatidic acid by glycerolphosphate acyltransferase GPAT. Phospholipid Synthesis Synthesis of all classes of phospholipids begins with two common precursors: phosphatidic acid and diacylglycerol Figure 3. It is also a precursor for phosphatidic acid, lysophosphatidylcholine and platelet-activating factor , each with important signalling functions, and of phosphatidylserine.
Broadly speaking, lipids can be classified into five major subcategories.
Lysophosphatidylcholine Lysophosphatidylcholine LPC , with one mole of fatty acid per mole of lipid in position sn-1, is found in trace amounts in most animal tissues at greater concentrations, it disrupts membranes. Triacylglycerol Transport While TAG synthesis can take place in the brain, liver, heart, skeletal muscle and kidney, they are also transported to these regions through the bloodstream. The addition of phosphocholine defines these lipids as phospholipids, and they are therefore also referred to as phosphosphingolipids. Thus, protein-dependent intracellular transport does not appear to be a major contributor to phospholipid redistribution. Fission of the vesicles with the plasma membrane transfers the lipid cargo from one membrane to another. The monoacylglycerol pathway is similar, but rather than initiating with glucose, this pathway begins with monoacylglycerol, which is converted into 1,2-diacylgycerol by monoacylglycerol acyltransferase MGAT.
In this review, we discuss their individual structure, synthesis, and transport in the context of brain function. Another variation, although rare in humans, is the branching, or functionalization, of the fatty acid chain.