Triacylglycerol assembly from binary mixtures of fatty acids byApiotrichum curvatum

To observe how the stereospecific distribution of acyl groups in triglycerides is affected by the composition of fatty acids available for esterification, the oleaginous yeastApiotrichum curvatum was grown on various binary mixture of palmitic, stearic, oleic and linoleic acids as carbon sources, and the yeast triglycerides were analyzed. When oleic acid‐linoleic acid mixtures in various ratios were used as substrates, the yeast grew well, and the composition of the intracellular triglycerides reflected the substrate composition, but more linoleate than oleate was deposited in the triglycerides. Oleate was favored over linoleate at thesn‐2 position of the glycerol. With substrates containing palmitic and stearic acids, the yeast accumulated less oil, and incorporation of stearic acid into the triglycerides also was very limited. When mixtures of palmitic acid‐oleic acid and palmitic acid‐linoleic acid were used as substrates, the yeast triglyceride composition did not reflect that of the substrate, and the accumulation in the yeast of the unsaturated acid in the substrate was favored. Possibly, the yeast had more limited access to solid than to liquid substrates. For oleic acid‐linoleic acid substrates, when the percentages of oleate and linoleate at the three glycerol positions were plottedvs. the percentage of these acyl groups in the total triglyceride, apparent linear relations were observed for most of the range, and the sums of the intercepts and slopes of the three lines for each acyl group were 0 and 3, respectively. Two mathematical models of triglyceride assembly are proposed, both of which fit the experimental data. One model assumes that for a certain proportion of the glycerol molecules, the acyl composition of the threesn positions is rigidly controlled independently of the substrate concentration. The other assumes that the various acyl groups are distributed on the threesn positions of glycerol with different affinities.