Fatty acids, labeling

The authors have also synthesized134 fatty acids labelled with deuterium and carbon-11 in order to investigate if kinetic isotope effects related to fatty acid metabolism can be observed in vivo by pet133,135-137. In vitro, the large kinetic deuterium isotope effects are observed in the oxidation of deuteriated aliphatic carboxylic acids with alkaline permanganate and manganate135-139. 

In 1904, long before the advent of radioactive tracers, Knoop synthesized fatty acids labeled by chemical attachment of a benzene ring at the end opposite the carboxyl group. He prepared these compounds with both odd and even numbers of carbon atoms in straight chains and fed them to dogs. From the dogs urine he isolated hippuric acid and phenylaceturic acid, which are the amides of glycine with benzoic acid and phenylacetic acid, respectively. Knoop showed that the phenylacetic acid was produced from those fatty acids with an... 

Figure 4. Autoradiographs of red kidney bean 4 days after applications of Tween 20-,4C. Left, untreated middle, fatty acid labeled right, oxy-ethylene labeled. Both these fractions were from the main peak of the Sephaaex column elutions...

Fatty acid Label data (%) Found (% standard deviation) after saponification and esterification with ... 

Both straight-chain and branched fatty acids labelled with carbon-11 at carbon-1 have also been made with Hi iCN. Although these compounds have been made using a Grignard reagent the HUCN method 1 is superior because it can be done on a small scale and... 

This method has been used for unsaturated fatty acid labeling (Machulla, 1982), with a yield near 100%. The reactions are nonetheless rarely used nowadays substitution reactions are preferred. 

In the course of our metabolic studies with C -labeled polyenoic fatty acids, we also measured the expired radioactive CO2. Mead and his colleagues (6, 13) and Bernhard (14) have shown that hnoleic and linolenic acids are easily oxidized. In these authors experiments, acids labeled in the carboxy group or uniformly labeled compounds were used. With use of our unsaturated fatty acid labeled close to the methyl end, the appearance of radioactive COa is a valid test for the complete oxida tive degradation of the acid. In any case, the active CO2 can appear only after the oxidation has passed the whole double bond system. 

Draw the structure of a typical saturated fatty acid. Label the polar and nonpolar portions of the molecule. Whieh portion is hydrophobic Hydrophilic ... 

When preparing fatty acids labelled with it is usual to incorporate the label as late in the synthesis as possible and preferably in a reaction proceeding in high yield. and " C02 (from labelled carbo-... 

Fatty acids labelled non-specifically can be obtained from plants or photosynthetically active micro-... 

Acetate is frequently used to label the fatty acyl moieties of phospholipids. Galliard (1972) employed this property in preparing radioactive phospholipids in potato tuber slices PC and neutral lipids were the major fractions labeled, and the fatty acids labeled in PC were 16 0 (22.5%), 18 0 (11.4%), 18 1 (30.4%), and 18 2 (32.6%) after a 2-h incubation at 25°C. 

A study of the exchange of fatty acids, labeled from [ C]acetate, between potato microsomes and mitochondria (Mazliak and Ben Abdelkader, 1971) showed that all types of fatty acids were transferred, the major ones being the most extensively exchanged. There was no breeikdown of fatty acids and no subsequent synthesis during the transfer, since the distribution of C radioactivity remained constant among the various fatty acids in the donor and the acceptor fractions. 

Knoop fed rabbits fatty acids labeled with a phenyl group at the methyl terminal (co-carbon, see Figure 1). The bond between the phenyl group and the methyl group cannot be attacked by... 

The case for the participation of intravascular lipolysis by lipoprotein lipase seems to be quite impressive. The quantitative importance of this process for chylomicron removal is, however, less clear. An attempt to arrive at a quantitative estimate has been based on the infusion into a dog, at constant rate over a two hour period, of fatty acid labelled chylomicra. The specific activity of the free fatty acid fraction reached a constant level of around 10% of the infused chylomicron glyceride fatty acids (Fredrickson et al. 1958b). This finding indicates that at most one tenth of the free fatty acids in the plasma are derived from intravascular splitting of chylomicra. If free fatty acids were the sole lipid substance available to the tissues, one would expect that formation from radioactive triglyceri-... 

Not all of the chylomicron triglycerides have to pass through the liver and recycle in the blood as lipoproteins, in order to be incorporated in adipose tissue. A part of the chylomicron triglycerides may be taken up directly. This depends on the nutritional state of the animal. When fatty acid labelled chylomicra are injected into a fasting animal only small amounts can be discovered in adipose tissue, short intervals after the injection. However, if this experiment is performed with a carbohydrate fed animal, as much as 25% can be found in adipose tissue after short periods (Bragdon and Gordon 1958). 

When a suitably labelled precursor is administered to an animal, the label appears in the glycerophosphatides of most tissues. This is true for a wide variety of precursors, including orthophosphate labelled with fatty acid labelled with H, or elaidic acid acetate labelled with or glycerol labelled with... 

Two batches of seedlings were incubated with (l-14C)acetate for 30 min, with or without 2pM monensin respectively. After homogenization and density gradient subfractionation of the microsomal pellets, the total lipid and fatty acid labels were determined. 

The specific radioactivities of lipids and fatty acids from each previously characterized fraction (2, 3) were calculated. Monensin leads to an accumulation of neosynthesized lipids in a Golgi-enriched fraction. Moreover, in the presence of monensin, the fatty acid label, analyzed by radio - glc, exhibits a much more important accumulation in this fraction (see table 1). 

Plant Lipid % Tbtal Lipid Label Fatty Acids (% total fatty acid label) ... 

Fig. 6 Specific radioactivities of individual fatty acids labelled from... 

Fatty acids labeled in an odd carbon give rise, in general, to acetoacetate with isotope only in the carbonyl (C 0) and carboxyl carbons (C OOH). The relative incorporation of isotope into these carbons is conveniently represented by the C 0 C 00H ratio. Since acetoacetate is formed by the condensation of 2-carbon fragments, the C 0 C OOH ratio is a measure of the relative incorporation of carboxyl-labeled isotopic 2-carbon fragments into the carbonyl (CHtC 0) and carboxyl (—CH C OOH) moieties of acetoacetate. 

This degradation procedure would not be applicable for determining the relative incorporation of isotope into the carbonyl and carboxyl moieties of acetoacetate labeled in the a- and 7-carbons (C HjCOC H2-COOH). The simplicity of the decarboxylation procedure no doubt accounts for the popularity of the use of fatty acids labeled in an odd carbon. 

Effect of Position or Fatty Acid Label on the C 0 C 00H Ratio or... 

R = C 0 C OOH ratio for the fatty acid labeled in any other odd carbon... 

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