Triacylglycerols from bovine milk fat were fractionated by reversed-phase liquid chromatography. The fatty acid and triacylglycerol compositions of each fraction were determined by capillary gas chromatography. These data were used to determine the accurate proportions of 223 individual molecular species of even-numbered triacylglycerols, accounting for 80% of total triacylglycerols (all percentages are expressed as moles per 100 mol). The three major triacylglycerols were butyroylpalmitoylacylglycerols, namely butyroylpalmitoyloleoylglycerol (4.2%), butyroyldipalmitoylglycerol (3.2%), and butyroylmyristoylpalmitoylglycerol (3.1%). Twenty-two triacylglycerols (> 1%) contained at least two of the four major long-chain fatty acids (C14:0, C16:0, C18:0, and C18:1). Among them were eight butyroyldiacylglycerols, the proportions of which reached 19% in total but only 12% when calculated on the basis of a random distribution of the fatty acids in the triacylglycerol molecules. More generally, most of the triacylglycerols that are composed of a short-chain fatty acid (C4:0 or C6:0) and two fatty acids in the range of C12 to C18 are preferentially synthesized by the mammary gland; their proportions (36% in total) were higher than the corresponding random values (24% in total). Conversely, the total amounts of simple (.4%) and mixed (2.9%) saturated long-chain (C14:0 to C18:0) triacylglycerols were much lower than those expected from random calculation (1.9 and 6.1%, respectively).

Summary ― Essential fatty acids (EFA), which are not synthesized in animal and human tissues, belong to the n-6 and n-3 families of polyunsaturated fatty acids (PUFA), derived from linoleic acid (LA,) and a-linolenic acid (LNA,. Optimal requirements are 3-6% of ingested energy for LA and 0.5-1% for LNA in adults. Requirements in LNA are higher in development. Dietary sources of LA and LNA are principally plants, while arachidonic acid (AA,) is found in products from terrestrian animals, and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)

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The movement of alpha-linolenic acid (C18:3, n-3) through the mitochondrial outer membrane to oxidation sites was studied in rat liver and compared with the movement of linoleic acid (C18:2, n-6) and oleic acid (C18:1, n-9). All differ in the degree of unsaturation, but have the same chain length and the same position of the first double bond when counted from the carboxyl end. The following results were obtained. (1) The overall beta-oxidation in total mitochondria was in the order C18:3, n-3 greater than C18:2, n-6 greater than C18:1, n-9, independent of the amount of albumin in the medium. (2) The rate of formation of acylcarnitine from acyl-CoA was higher with oleoyl-CoA than with linoleoyl-CoA, and remained very low with alpha-linolenoyl-CoA for all concentrations studied. (3) When the formation of acylcarnitines originated from fatty acids (as potassium salts) in a medium containing CoA and ATP, the conversion of alpha-linolenate was greater than that of linoleate, which in turn was greater than that of oleate. (4) Use of a more purified mitochondrial fraction, practically devoid of peroxisomes, did not modify the results obtained with alpha-linolenate. (5) alpha-Linolenoyl-CoA did not inhibit oxidation of labelled alpha-linolenate, whereas the other acyl-CoAs did. (6) Transfer to carnitine of all three fatty acids (as potassium salts) by carnitine palmitoyltransferase-I (CPT-I) was similarly inhibited by increasing concentrations of malonyl-CoA. (7) On using a fraction containing mitochondrial outer membranes, the formation of acylcarnitines from potassium salts of fatty acids was qualitatively and quantitatively similar to that found with whole mitochondria. (8) Our observations show that alpha-linolenoyl-CoA synthesized other than in the mitochondria cannot be used to any great extent by the mitochondria due to its configuration. However when added as the unactivated form, alpha-linolenate appears to be very quickly oxidized, but should first be activated by acyl-CoA synthetase in the mitochondrion itself. Then it is rapidly channelled to CPT-I. These enzymic sites are probably close together in the mitochondrial outer membrane. The different behaviour of the alpha-linolenic group compared with the other acyl groups in the studied pathway can be explained by a different spatial arrangement due to the number and position of the double bonds.

Triglycerides of coconut oil were fractionated by GLC into 13 groups based on their carbon numbers of 28 to 52. These groups represent 99.8% of the total glycerides of coconut oil. With the fatty acid composition of each group, it was possible to calculate the composition of 79 types of triglycerides. These types are defined by the nature of their constitutive fatty acids but the position of the acids on glycerol is unknown. Each group usually has only one major type of triglyceride. For example, group 36 has 52% of trilaurin. Also four types of triglycerides comprise 42.4% of the total glycerides and 24 types comprise 85%. The experimentally found distributions in each group are compared to the random distributions calculated from the fatty acid composition. For groups with carbon numbers 38 and 40, the experimental and random distributions were very similar but for most other groups, the distributions found were much different from the calculated random distributions.

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Age-related changes in delta 6 desaturation of [1-14C]alpha-linolenic acid and [1-14C]linoleic acid and in delta 5 desaturation of [2-14C]dihomo-gamma-linolenic acid were studied in liver microsomes from Wistar male rats at various ages ranging from 1.5 to 24 mon. Desaturase activities were expressed both as specific activity of liver microsomes and as the capacity of whole liver to desaturate by taking into account the total amount of liver microsomal protein. delta 6 Desaturation of alpha-linolenic acid increased from 1.5 to 3 mon and then decreased linearly up to 24 mon to reach the same desaturation capacity of liver measured at 1.5 mon. The capacity of liver to desaturate linoleic acid increased up to 6 mon and then remained constant, whereas microsomal specific activity was equal at 1.5 and 24 mon of age. The capacity of liver to convert dihomo-gamma-linolenic acid to arachidonic acid by delta 5 desaturation decreased markedly from 1.5 to 3 mon. It then increased to reach, at 24 mon, the same level as that observed at 1.5 mon. Age-related changes in the fatty acid composition of liver microsomal phospholipids at the seven time points studied and of erythrocyte lipids at 1.5 and 24 mon were consistent with the variations in desaturation capacity of liver. In particular, arachidonic acid content in old rats was slightly higher than in young rats whereas contents in linoleic and docosahexaenoic acids varied little throughout the life span.(ABSTRACT TRUNCATED AT 250 WORDS)

Purified triacylglycerols (TAG) fromPinus koraiensis andP. pinaster seed oils, which are interesting and commercially available sources of Δ5‐olefinic acids (i.e.,cis‐5,cis‐9,cis‐12 18:3 andcis‐5,cis‐11,cis‐14 20:3 acids) were fractionated by reversed‐phase high‐performance liquid chromatography, and each fraction was examined by capillary gas‐liquid chromatography for its fatty acid composition. A structure could be assigned to more than 92% of TAG from both oils. In both instances, ca. 48% of the TAG were shown to contain at least one δ5‐olefinic acid. In the great majority of TAG, our data showed that there is only one molecule of δ5‐olefinic acid per molecule of TAG. This is compatible with theoretical calculations based on the proportion of total δ5‐olefinic in the oils. Thecis‐5,cis‐9,cis‐12 18:3 acid (14.2 and 8.6% of total fatty acids in the seed oils ofP. koraiensis andP. pinaster, respectively) and thecis‐5,cis‐11,cis‐14 20:3 acid (1.1 and 8.1% of total fatty acids in the seed oils ofP. koraiensis andP. pinaster, respectively) are preferentially associated with two molecules of linoleic acid, and to a lesser extent, to one molecule of linoleic acid and one molecule of oleic acid, or two oleic acid molecules. However, several other combinations occur, each in low amounts. The distribution of δ5‐olefinic acids in TAG is evidently not random. Combining these results with the known preferential esterification of δ5‐olefinic acids to the 1,3‐positions of TAG would suggest that most of these acids are present at only one of these positions at a time.