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

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.

Mechanisms of temperature adaptation in poikilotherms

“…On investigation, we found that oxygen availability (independent of temperature) could regulate the de novo synthesis of oleate desaturase protein [44,45]. We also found that oxygen availability could limit the activity of pre‐existing oleate desaturase in A. castellanii [45].…”

Apoptosis of Acanthamoeba castellanii Trophozoites Induced by Oleic Acid

“…; Rutter et al. ). Other studies have shown that LA and OA are the most active uncouplers and protonophores in A. castellanii mitochondria (Swida et al.…”

“…This may be because A. castellanii used the excess OA to synthesize a range of polyunsaturated fatty acids (Rutter et al. ) catalyzed by the fatty acid n‐6 desaturase; or used OA as a substrate to esterify phospholipids through catalysis by Δ12,Δ15‐desaturase (Sayanova et al. ).…”

“…This physiological distribution of FAs suggests that OA and AA may play important roles in protozoan growth and metabolism. As a precursor, OA can be used to synthesize linoleic acid (LA) and a series of n-6 polyunsaturated fatty acids in A. castellanii trophozoites (Jones et al 1990;Rutter et al 2002). Other studies have shown that LA and OA are the most active uncouplers and protonophores in A. castellanii mitochondria (Swida et al 2007), and are involved in lowering of the yield of oxidative phosphorylation (Jarmuszkiewicz et al 2000).…”

“…The levels of caspase and autophagy-related proteins increased in the first 3 h of treatment with OA, but there was no significant difference from controls after 12 h of treatment. This may be because A. castellanii used the excess OA to synthesize a range of polyunsaturated fatty acids (Rutter et al 2002) catalyzed by the fatty acid n-6 desaturase; or used OA as a substrate to esterify phospholipids through catalysis by D12,D15-desaturase (Sayanova et al 2006).…”