INITIAL STEPS OF SOPHOROSELIPID BIOSYNTHESIS BY CANDIDA-BOMBICOLA ATCC-22214 GROWN ON GLUCOSE

Candida bombicola ATCC 22214 produces the glycolipid sophoroselipid wh en cultivated on a medium with glucose as the sole carbon source. Unde r phosphate-limiting conditions the product yield rises from 0.033 to 0.143 and the specific product formation rate rises from 0.004 h(-1) t o 0.007 h(-1). Enhanced sophoroselipid synthesis is initiated by the d ecline of the specific activities of NAD- and NADP-dependent isocitrat e dehydrogenase (EC 1.1.1.41 and 1.1.1.42) to 2% and 0% of the initial activities respectively. Constantly high specific activity of citrate synthase (EC 4.1.3.7) causes an accumulation of isocitrate and citrat e in the mitochondria. Both acids are transported into the cytosol whe re citrate is cleaved by ATP: citrate lyase (EC 4.1.3.8) giving rise t o acetyl-CoA, the precursor of fatty acid synthesis. The ATP: citrate lyase is unaffected by different energy charges; the apparent K-m valu es for coenzyme A, ATP and citrate are 23 mu M, 250 mu M and 256 mu M respectively. NADPH for fatty acid synthesis might be generated by fur ther metabolism of oxaloacetate, the other product of the citrate-clea ving reaction, by oxidation of the isocitrate by the cytosolic NADP-de pendent isocitrate dehydrogenase or via the hexose monophosphate shunt . A possible explanation for sophoroselipid formation during exponenti al growth is given.