Oxygen induction of a novel fatty acid n−6 desaturase in the soil protozoon, Acanthamoeba castellanii

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Abstract
Induction of fatty acid desaturation is very important for the temperature adaptation of poikilotherms. However, in oxygen-limited late-exponential-phase Acanthamoebacastellanii cultures, oxygen alone was able to induce increased activity of a fatty acid desaturase that converts oleate into linoleate and which has been implicated in the temperature adaptation of this organism. Experiments with Δ10-nonadecenoate showed that the enzyme is an n-6 desaturase rather than a Δ12-desaturase. It also used preferentially 1-acyl-2-oleoyl-phosphatidylcholine as substrate and NAD(P)H as electron donor. The involvement of cytochrome b5 as an intermediate electron carrier was shown by difference spectra measurements and anti-(cytochrome b5) antibody experiments. Of the three protein components of the desaturase complex, oxygen only increased the activity of the terminal (cyanide-sensitive) protein during n-6 desaturase induction. The induction of this terminal protein paralleled well the increase in overall oleate n-6 desaturation. The ability of oxygen to induce oleate desaturase independently of temperature in this lower eukaryotic animal model is of novel intrinsic interest, as well as being important for the design of future experiments to determine the molecular mechanism of temperature adaptation in poikilotherms.