Bicarbonate stimulates stearate synthesis in chloroplasts: discrimination against stearate in the biosynthesis of glycerolipids
1993
Sanchez, J. | Mudd, J.B.
The effects of increasing concentrations of bicarbonate on the incorporation of 14C-acetate into fatty acids, and the distribution among acyl lipid classes by spinach (Spinacea oleracea) chloroplasts have been studied. Stimulation of the total incorporation of 14C-acetate in the presence of small concentrations of bicarbonate was observed, but higher concentrations showed inhibition when compared with the optimum which was found to be 5 mM. The incorporation of newly synthesized fatty acids into phosphatidylglycerol was lowered in the presence of bicarbonate, whereas an increase in the incorporation into diacylglycerols was observed. High concentrations of bicarbonate in the incubation medium resulted in the accumulation of radioactivity in stearic acid with a concomitant decrease in the formation of oleic acid. This effect was reversed when dihydroxyacetone phosphate, oxalacetate and Pi (DHAP shuttle), or dichlorophenolindophenol and ascorbate were added to the incubation mixture. Radioactive stearate was found to accumulate in the free fatty acid fraction as well as in acylthioesters, monoacylglycerols, phosphatidic acid and diacylglycerol, but it was discriminated against in the synthesis of monogalactosyldiacylglycerol, phosphatidylcholine and phosphatidylglycerol.
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