Metabolism of Palmitate Differs in Neurospora Crassa Mutants with Impaired Fatty Acid Synthase

Abstract

Fatty acid metabolism in the fungus Neurospora crassa resembles that in higher plants. Neurospora additionally has the advantages of microbial systems, allowing biochemical and genetic studies of the metabolism of both common and unusual fatty acids. The Neurospora cel mutant is impaired in fatty acid synthase, and requires supplementation with palmitate (16:0) for growth. By following metabolism of exogenous [2H]16:0 using GC/MS, we have observed that wild-type Neurospora only poorly converts exogenous 16:0 to unsaturated fatty acids. In contrast, cel readily converts 16:0 to the usual major fatty acids formed by Neurospora, 18:0, 18:1Δ9, 18:2Δ9,12 and 18:3Δ9,12,15. It also forms high levels of two other fatty acids not normally observed in Neurospora. Addition of the cyclopropane fatty acid dihydrosterculate suppresses formation of these fatty acids in cel. This altered metabolism of exogenous 16:0 may be directly due to impaired flux through the endogenous biosynthetic pathway, or may result from altered regulation of the synthesis of unsaturates in the mutant.