J. Biol. Chem., Vol. 262, Issue 16, 7586-7593, 06, 1987
On the metabolic relationships between monogalactosyldiacylglycerol and digalactosyldiacylglycerol molecular species in Dunaliella salina
SH Cho and GA Thompson Jr
Dunaliella salina cells were pulse-labeled for 2 min with [14C]palmitic
acid, [14C]oleic acid, or [14C]lauric acid in order to trace the pathway of
galactolipid biosynthesis and desaturation. Through the use of high
performance liquid chromatography it was possible to follow the movement of
radioactivity through many individual molecular species of
monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG)
for periods of 24 h and, in some cases, as much as 120 h. Analysis of the
fatty acid fluxes permitted us to refine current views regarding
biosynthesis of the predominantly "prokaryotic" galactolipids. The initial
D. salina MGDG molecular species, containing paired oleate and palmitate
(18:1/16:0), can follow two metabolic routes. If the palmitoyl chain is
desaturated to 16:1, the resulting 18:1/16:1 MGDG is subject to rapid
further desaturation to varying degrees, and a part of these products is
subsequently galactosylated to DGDG. Contrary to widely held opinions,
these DGDG molecular species can themselves be further desaturated toward a
18:3/16:4 final product. In a separate series of reactions, a smaller
portion of the nascent 18:1/16:0 MGDG is directly galactosylated to
18:1/16:0 DGDG. This molecular species can then be sequentially desaturated
to 18:2/16:0 DGDG and 18:3/16:0 DGDG. However, there is only very limited
desaturation of the palmitoyl group attached to these molecular species.
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