Pathways for desaturation of oleoyl chains in Candida lipolytica.

Incubation of microsomes from 25 degrees C- or 10 degrees C-grown cells of Candida lipolytica with [14C]oleoyl-CoA ( [14C]18:1-CoA) in the presence or absence of NADH resulted in rapid acyl transfer of [14C]18:1 to phospholipids (mainly phosphatidylcholine (PC) and phosphatidylethanolamine (PE) and to acylglycerols. Incorporation into PC was greatly enhanced when incubation was carried out in presence of lysophosphatidylcholine (lyso-PC). In all experiments, in the presence of NADH and O2, with and without added lyso-PC, the initial rate of formation of [14C]linoleoyl-PC was much greater than that of [14C]linoleoyl-CoA ( [14C]18:2-CoA). These results suggest that the actual substrate for the delta 12-desaturase is the oleoyl-PC, although some desaturation of 18:1-CoA cannot be eliminated. It is concluded that the main pathway for 18:2 formation proceeds from stearoyl-CoA (18:0-CoA) leads to 18:1-CoA leads to 18:1-phospholipid leads to 18:2-phospholipid; the pathway 18:0-CoA leads to 18:1-CoA leads to 18:2-CoA leads to 18:2-phospholipid is a minor pathway. Microsomes from cells grown at 10 degrees C had a higher content of 18:2 and a lower phospholipid desaturase activity at 25 degrees C than microsomes from cells grown at 25 degrees C, suggesting an inverse relationship between desaturase activity and membrane lipid fluidity.