Differential alteration of delta 9 and delta 6 desaturation of fatty acids in rat brain preparations in vitro.

Developing rat brain has the capacity for either delta 9 or delta 6 desaturation of fatty acids. In liver, evidence supports the existence of separate enzymes for each reaction, but it is not known whether in brain delta 9 or delta 6 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 delta 9 position or in the delta 6 position. In addition, differential alteration of desaturation of palmitic acid, a substrate that can be desaturated in either the delta 9 or delta 6 positions by brain preparations from neonatal rats, was examined. Sterculate reduced delta 9 desaturation of palmitate 80--90% but reduced delta 6 desaturation only 35%. In contrast, linoleic acid preferentially reduced delta 6 desaturation of palmitate. Thus, delta 9 desaturation of saturated fatty acids appears to be catalyzed by an enzyme or enzyme site distinct from that for delta 6 desaturation. Accordingly, these activities may be independently regulated during crucial stages of brain development.