Fatty acid chain elongation rates

Cultured heart cells responded rapidly to fatty acids administered to the medium. Heated fat produced lower levels of unsaturated fatty acids in the PL fractions, and a greatly increased level of arachidonic acid in the TG fractions (15) In the livers of rats fed heated fats, Rao et al. (50) showed a rapid rate of elongation and desaturation of fatty acid chains. 

Intestinal Handling of FFA In the cells of the small intestine, several enzymes can act on free but not on esterified fatty acids. In contrast to MAGs, FFA are diluted with fatty acids originating from the plasma free fatty acid pool (44). After activation they can be oxidized, elongated, chain desaturated, and converted into complex lipids (45, 46). The relative rates depend on the nature of the fatty acids and on the presence of other components in the intestinal cells (47). Conversion of saturated fatty acids in monounsaturated ones when they are absorbed as FFA, i.e., when they were present in the outer position of the dietary TAGs, could... 

Rates of Component Reactions in the Microsomal Chain Elongation of Fatty Acids Using Livers from Rats Raised on a Normal Chow or Fat Free Diet ... 

Under normal dietary conditions liver lipids contain high levels of linoleate and arachidonate but only trace or negligible amounts of other acids in this metabolic sequence. We have measured rates of both desaturation and chain elongation reactions in the linoleate sequence to determine what relationship exists between rates of conversion and the type of fatty acid found in liver lipids (Bernert Sprecher, 1975). Dietary linoleate is either incorporated into liver lipids, or as shown in Figure 1, it is desaturated to 6,9,12-18 3 at a rate of 1.0 nmole/min/mg microsomal protein. Liver lipids never contain measureable amounts of 6,9,12-18 3 even when this acid is added directly to the diet... 

FIGURE 1. Rates of desaturation and chain elongation for acids in the linoleate sequence. Rates expressed as nmoles product/ min/mg microsomal protein. Each incubation for desaturation contained 10 ymoles ATP, 2 ymoles NADH, 0.3 ymole CoA, 150 ymoles potassium phosphate buffer, pH 7.4, 150 nmoles radioactive fatty acid, 5 mg liver microsomal protein from rats raised on a fat-free diet and 5 mg bovine serum albumin. Chain elongation conditions were the same except 2.0 ymoles of NADPH were used instead of NADH and 0.3 ymole of malonyl-CoA was added. All incubations were run in 1.5 ml for 3 minutes at 37°C. (Bernert Sprecher, 1975)... 

Even when rats are raised on a fat free diet the liver lipids do not contain high levels of polyunsaturated fatty acids derived from palmitoleate. On the basis of structure this is somewhat surprising since the metabolites from 18 2 to 20 4 in the palmitoleate sequence differ from those in the linoleate sequence only in that the double bond is shifted one position closer to the carboxyl carbon. The rates of desaturation and chain elongation of acids in the palmitoleate sequence are shown in Figure 4,... 

Within any given unsaturated fatty acid biosynthetic sequence the rates of chain elongation generally proceed more rapidly than... 

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