TRIACYLGLYCEROL ASSEMBLY FROM BINARY-MIXTURES OF FATTY-ACIDS BY APIOTRICHUM-CURVATUM

To observe how the stereospecific distribution of acyl groups in trigl ycerides is affected by the composition of fatty acids available for e sterification, the oleaginous yeast Apiotrichum curvatum was grown on various binary mixtures of palmitic, stearic, oleic and linoleic acids as carbon sources, and the yeast triglycerides were analyzed. When ol eic acid-linoleic acid mixtures in various ratios were used as substra tes, the yeast grew well, and the composition of the intracellular tri glycerides reflected the substrate composition, but more linoleate tha n oleate was deposited in the triglycerides. Oleate was favored over l inoleate at the sn-2 position of the glycerol. With substrates contain ing palmitic and stearic acids, the yeast accumulated less oil, and in corporation bf stearic acid into the triglycerides also was very limit ed. When mixtures of palmitic acid-oleic acid and palmitic acid-linole ic acid were used as substrates, the yeast triglyceride composition di d not reflect that of the substrate, and the accumulation in the yeast of the unsaturated acid in the substrate was favored. Possibly, the y east had more limited access to solid than to liquid substrates. For o leic acid-linoleic acid substrates, when the percentages of oleate and linoleate at the three glycerol positions were plotted vs. the percen tage of these acyl groups in the total triglyceride, apparent linear r elations were observed for most of the range, and the sums of the inte rcepts and slopes of the three lines for each acyl group were 0 and 3, respectively. Two mathematical models of triglyceride assembly are pr oposed, both of which fit the experimental data. One model assumes tha t for a certain proportion of the glycerol molecules, the acyl composi tion of the three sn positions is rigidly controlled independently of the substrate concentration. The other assumes that the various acyl g roups are distributed on the three sn, positions of glycerol with diff erent affinities.