Desaturation unsaturated fatty acids rates

Cultured heart cells responded rapidly to fatty acids administered to the medium. Heated fat produced lower levels of unsaturated fatty acids in the PL fractions, and a greatly increased level of arachidonic acid in the TG fractions (15) In the livers of rats fed heated fats, Rao et al. (50) showed a rapid rate of elongation and desaturation of fatty acid chains. 

Therefore, high levels of unsaturated fatty acids in MGDG are due primarily to the rapid phase of desaturation. The desaturase shows normal kinetics, indicating higher rates of desaturation at higher temperatures. This suggests that the high levels of unsaturated fatty acids found at low temperatures are not due to increased enzyme activities because of an increase in O2 concentration nor abnormal enzyme kinetics. 

Our data show that plants have evolved a low temperature-induced desaturation (LTD) process that results in the very rapid desaturation of fatty acids of newly formed lipids [3]. This is followed by a much slower basm level desaturation (BLD). The two processes result in a final level of desaturation that is determined by a balance between the level of the rapid initial phase and the subsequent slower BUD. We can show that the LTD is induced at low temperature but is thermolabile at high temperatures, thus providing a mechanism for controlling the rate of desaturation of newly formed lipid. The loss and induction of desaturase activity is much more rapid than the changes in level of unsaturation of the bulk membrane lipid. We beueve that it is the control of desaturation of newly formed lipid which allows the plant to respond slowly to the environmental temperature over extended periods of time rather than to react immediately to transient fluctuations in diurnal temperature. 

We have previously shown [2] that the desaturation in MGDG and PC in leaves is dependent on the temperature at which the plants are grown. The rate of desaturation was determined from the rate of conversion of radioactive saturated to unsaturated fatty acids. We showed that plants... 

The results, therefore, confirm the trend to higher levels of unsaturation at lower temperatures but also suggest that the chloroplastic pathway is favoured, almost to the exclusion of the cytosolic pathway at temperatures of 10°C or lower. This means that C02 tracer techniques may be used in plants grown at 10°C to determine rates of biosynthesis and fatty acid desaturation of 16/18C molecular species (through the chloroplastic pathway) with little interference from accumulation of radioactivity through the cytosolic pathway. 

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