Some properties, including the substrate in vivo, of the Δ9-desaturase in Micrococcus cryophilus

The delta 9-desaturase of the psychrophilic bacterium Micrococcus cryophilus is shown to be a membrane-bound enzyme that is probably linked to a cyanide- (and azide-) sensitive respiratory chain with oxygen as the final acceptor. It has a pH optimum of 8.7 and contains an essential thiol group, but has no special ion requirements. The desaturase activity of washed membranes could not be increased by adding supernatant or NADH and NADPH, possibly owing to the endogenous generation of reduced cofactors by the membranes. The substrate for the desaturase is not acyl-CoA and is probably not acyl-acyl-carrier protein. Evidence is presented that the substrate in vivo is saturated phospholipid and a scheme for the possible routes of incorporation of exogenous stearic acid into oleoyl-phospholipid is presented.