Control of acyl lipid desaturation in the yeast Rhodotorula gracilis via the use of the cyclopropenoid fatty acid, sterculate

Summary

The effect of the cyclopropene fatty acid, sterculic acid, on fatty acid metabolism in the oleaginous yeast Rhodotorula gracilis (CBS 3043) has been studied. Sterculate caused approximately 90% inhibition of [1-¹⁴C]sterate desaturation but only about 25% inhibition when [1-¹⁴C]acetate was used as precursor. Measurement of acyl-coenzyme A (CoA) pool labelling and the pattern of distribution of radioactivity within lipid classes suggested that the high rate of inhibition of stearate desaturation was due to sterculate reducing the formation of stearoyl-CoA. In agreement with previous suggestions for plant and animal systems, experiments with a post-mitochondrial (20 000 g × 30 min) supernatant suggested that sterculoyl-CoA was the active inhibitor. The action of sterculate on endogenous lipid composition was most marked in stationary-phase cells. In such cells an increase in stearate was seen especially in the triacylglycerol pools, while α-linolenate was increased predominantly in the phospholipid fractions. The increased flux of carbon to α-linolenate at the same time that stearate desaturation appeared to be inhibited by sterculate, indicated that that two separate pathways for desaturation, employing different substrates, may operate in R. gracilis. We suggest that sterculate inhibits the stearoyl-(acyl-)CoA-dependent pathway but has little effect when phospholipids are used as substrates for acyl chain desaturation.