Malic enzyme (ME) catalyses the oxidative decarboxylation of L-malate to pyruvate and provides NADPH for intracellular metabolism, such as fatty acid synthesis. Here, the mitochondrial ME (mME) gene from Mortierella alpina was homologously over-expressed. Compared with controls, fungal arachidonic acid (ARA; 20:4 n-6) content increased by 60 % without affecting the total fatty acid content. Our results suggest that enhancing mME activity may be an effective mean to increase industrial production of ARA in M. alpina.

The fatty acid desaturase (FADS9-III) gene from M. alpina ATCC 32222 was cloned and overexpressed in a homologous system. Lipid analysis via GC-MS revealed that the D9-III fatty acid desaturase had moderate activity with palmitic acid (C16:0) and stearic acid (C18:0) as substrates. Palmitoleic acid (C16:1) and oleic acid (C18:1) contents increased 4.0-and 1.94-fold in the FADS9-III overexpression clones compared to the wild-type strain. Low temperature (12°C) significantly improved the conversion ratio of C16:0 to C16:1 (9.12-fold increase). In addition, the FADS9-III fatty acid desaturase had specific activity at the v9 position with lignoceric acid (C24:0) as a substrate.Practical applications: Our results indicate that FADS9-III prefers stearic acid (C18:0) and palmitic acid (C16:0) as substrates and has v9 fatty acid desaturase activity on lignoceric acid (C24:0). The conversion ratio of C24:0 to C24:1 reached 17% by supplementation of C24:0 in the medium at low temperature. The M. alpina v9 fatty acid desaturase (FADS9-III) is valuable for the production of mono-unsaturated fatty acids with a double bond at the v9 position.

Linoleic acid (LA) was extracted and purified from Idesia polycarpa Maxim.var. vestita Diels (IPMVVD) oil by urea adduction fractionation, and the response surface methodology (RSM) was successfully employed to optimize the process. The optimal conditions for purification of LA from mixed fatty acids by urea adduction fractionation were as follows: a weight ratio of 4.4:1.0:1.0 (w/w/w) of methanol/urea/mixed fatty acids, a temperature of -5°C and a time of 24.6 h, respectively. Under these conditions the experimental LA yield (48.65%) agreed with the predicted value and the purity of LA was 98.74%.