RAPID INDUCTION OF MICROSOMAL DELTA(12)(OMEGA-6)-DESATURASE ACTIVITY IN CHILLED ACANTHAMOEBA-CASTELLANII

The activity of microsomal DELTA12-desaturase in Acanthamoeba castella nii was increased after growing cultures were chilled from the optimal growth temperature (30-degrees-C) to 15-degrees-C. This increase was detectable in microsomes isolated from organisms subjected to only 10 min chilling. The mechanism of induction was investigated. The increas e in activity on chilling was greatly reduced when protein synthesis w as blocked before the temperature shift. Thus the major mechanism for the induction of DELTA12-desaturase is increased protein synthesis. DE LTA12-Desaturase activity was higher when assayed at 20-degrees-C than when assayed at 30-degrees-C, but these changes were not due to the i ncreased solubility of O2 at 20-degrees-C. The major substrate of DELT A12-desaturase was found to be 1-acyl-2-oleoyl phosphatidylcholine.