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

The activity of microsomal DELTA12-desaturase in Acanthamoeba castellanii 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 increase in activity on chilling was greatly reduced when protein synthesis was blocked before the temperature shift. Thus the major mechanism for the induction of DELTA12-desaturase is increased protein synthesis. DELTA12-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 increased solubility of O2 at 20-degrees-C. The major substrate of DELTA12-desaturase was found to be 1-acyl-2-oleoyl phosphatidylcholine.