Positional distribution of fatty acids in triglycerides of animal depot fats

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Several animal depot fats were subjected to stereospecific analysis, i.e., the fatty acid distribution in positions 1, 2, and 3 of the triglycerides were determined. The distribution of fatty acids among the positions 1, 2, and 3 in the triglycerides of animal depot fats is non-random. The distribution between position 2 and positions 1 and 3 seems to be governed by chain length and unsaturation. The shorter and the more unsaturated fatty acids show a greater tendency to occupy the position 2. This rule applies also to the apparent exceptions, the fats of pig and marine mammals, but in these the influence of chain length overrides that of unsaturation. On the other hand, in the three birds investigated unsaturation seems to be the only directing factor. We found fats with asymmetrical distribution of fatty acids as well as symmetrical fats. All mammalian fats were asymmetrical, as were the fats of one amphibian, one fish, and one arthropod, whereas the fats of one fish, one arthropod, and three birds were symmetrical. All asymmetrical fats have an excess of palmitic acid in position 1 and of oleic acid in position 3,