Differential alteration of Δ9 and Δ6 desaturation of fatty acids in rat brain preparations in vitro

Developing rat brain has the capacity for either Δ9 or Δ6 desaturation of fatty acids. In liver, evidence supports the existence of separate enzymes for each reaction, but it is not known whether in brain Δ9 or Δ6 desaturation of saturated fatty acids involves distinct enzymes. We have used fatty acids, including the cyclopropene fatty acid, sterculic acid, to alter desaturation activities with substrates that are desaturated predominantly in the Δ9 position or in the Δ6 position. In addition, differential alteration of desaturation of plamitic acid, a substrate that can be desaturated in either the Δ9 or Δ6 positions by brain preparations from neonatal rats, was examined. Sterculate reduced Δ9 desaturation of palmitate 80-90% but reduced Δ6 desaturation only 35%. In contrast, linoleic acid preferentially reduced Δ6 desaturation of palmitate. Thus, Δ9 desaturation of saturated fatty acids appears to be catalyzed by an enzyme or enzyme site distinct from that for Δ6 desaturation. Accordingly, these activities may be independently regulated during crucial stages of brain development.