Studies on the origin of milk fat. 1. The location of tritium in stearic acid produced by the catalytic addition of tritium to elaidic acid

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Abstract
Stearic acid labeled with tritium by catalytic addition, with a palladium-black catalyst, was fed to a goat, and the unsaturated fatty acids of the fat from 2 milk samples were separated by the lead-salt method. These were radioactive. From these unsaturated acids, after dilution with carrier oleic acid, dihydroxystearic acid was prepared and obtained in pure crystalline form. This was found to be radio-active, thus formally proving the biological conversion of stearic into oleic acid in the goat. The dihydroxystearic acid from each sample was decomposed into pelargonic aldehyde and azelaic semialdehyde. Complete recovery of the tritium originally in the dihydroxystearic acid was obtained with the limits of experimental error. The conclusion is drawn that the tritium in the dihydroxystearic acid was stably bound. It was found further that 1.68 times as much tritium was contained in the pelargonic aldehyde as in the azelaic semialdehyde. The 2 aldehydes were oxidized to the corresponding acids, thus labilizing the tritium originally attached to the C(9) and C(10) atoms. The loss of tritium was such that about 3% of the total tritium in the dihydroxystearic acid molecule must have been attached to the C(9) atom and 12% to the C(10) atom. The significance of these findings is discussed in the light of possible artifacts, and the conclusion is drawn that the original stearic acid was asymmetrically labeled and that only about 28% of the total tritium in the molecule was attached to the C atoms which were reduced.