Short-chain saturated phospholipid

The mitochondrial membranes are rich in phospholipids—principally phosphatidylcholine, phos-phatidylinositol and phosphatidylethanolamine (Figure 1.5). Cardiolipin (diphosphatidylglycerol), in minority in the plasmic membrane (Figure 1.4), is predominant in the inner mitochondrial membrane. The fatty acids of the mitochondrial phospholipids are in C16 0, C16 l, C18 0, C18 l. In aerobiosis, the unsaturated residues predominate. When the cells are grown in anaerobiosis, without Upid supplements, the short-chain saturated residues become predominant cardiolipin and phosphatidylethanolamine diminish whereas the proportion of phosphatidyUnositol increases. In aerobiosis, the temperature during the log phase of the cell influences the degree of unsaturation of the phospholipids- more saturated as the temperature decreases. 

The positional distribution of fatty acids in phosphatidylcholine and phosphatidylethanolamine, the major glycerophospholipids, of bovine milk, were investigated by Morrison et al. (1965) and are shown in Table 1.13. Unlike triacylglycerols, phospholipids do not contain short-chain fatty acids (14 0 being the shortest chain fatty acid present at a significant level). This is probably due to differences in the route of synthesis, as most short-chain fatty acids are found at the sn-3 position of triacylglycerols, which in phospholipids is occupied by the phosphate moiety. In phospholipids, the polyunsaturated fatty acids tend to be esterified preferentially at the sn-2 position, while the saturated fatty acids show a preference for the sn-1 position (Table 1.13). For phosphatidylethanolamine, 18 2 and 18 3 are found predominantly at the sn-2 position, while 18 1 is fairly evenly distributed and 16 0 and 18 0 are predominantly at the sn-1 position. In phosphatidylcholine, which is more saturated than phosphatidylethanolamine, the distribution of saturated and unsaturated fatty acids is less distinct between... 

The nature of a fatty add influences its fate. Short- and medium-tdiain fatty adds tend to be oxidised immediately to carbon dioxide, rather than deposited as TGs or phospholipids. The presence of double bonds ("unsaturations") in long-chain fatty adds influences the immediate fate of the add. Some evidence suggests that unsaturated fatty acids, such as 18 2, tend to be oxidized at a slightly faster rate in the hours following a meal than saturated fatty acids, such as 18 0 (Jones et al., 1985, Jones and Schoeller, 1988). More specifically, about 2% of a test meal of 18 0 may be oxidized in the 9 hours toUowing Ingestion, whereas about 10% of a test meal of 18 2 may be oxidized in the same period, The mechanisms that influence the fates of unsahirated and saturated fatty adds are only beginning to be understood. 

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