Biosynthetic utilization of photoreactive fatty acids by rat liver microsomes

The photoreactive ω-diazirinophenoxy derivatives of nonanoate, undecanoate, tridecanoate, and pentadecanoate were shown to be activated by rat liver microsomes to the corresponding acyl-CoA derivatives. The Km and Vmax for these fatty acid analogues were determined; the values obtained indicate that the addition of a photoreactive group to an alkyl chain has an effect similar to that of elongation of the chain by about seven carbons. Incubation of microsomes in the presence of lysophospholipids resulted in the incorporation of the photoreactive fatty acids into the corresponding phospholipids. The ability of mammalian systems to utilize these photoreactive fatty acids for phospholipid synthesis establishes their suitability as photoaffinity analogues of fatty acids.

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Effect of liver fatty acid binding protein on fatty acid movement between liposomes and rat liver microsomes

Biochemical Journal ◽

10.1042/bj2440717 ◽

1987 ◽

Vol 244 (3) ◽

pp. 717-723 ◽

Cited By ~ 36

Author(s):

M McCormack ◽

P Brecher

Keyword(s):

Fatty Acids ◽

Fatty Acid ◽

Rat Liver ◽

Equilibrium Dialysis ◽

Liver Microsomes ◽

Egg Yolk ◽

Fatty Acid Binding Proteins ◽

Rat Liver Microsomes ◽

Acid Complex ◽

Fatty Acid Binding

Although movement of fatty acids between bilayers can occur spontaneously, it has been postulated that intracellular movement is facilitated by a class of proteins named fatty acid binding proteins (FABP). In this study we have incorporated long chain fatty acids into multilamellar liposomes made of phosphatidylcholine, incubated them with rat liver microsomes containing an active acyl-CoA synthetase, and measured formation of acyl-CoA in the absence or presence of FABP purified from rat liver. FABP increased about 2-fold the accumulation of acyl-CoA when liposomes were the fatty acid donor. Using fatty acid incorporated into liposomes made either of egg yolk lecithin or of dipalmitoylphosphatidylcholine, it was found that the temperature dependence of acyl-CoA accumulation in the presence of FABP correlated with both the physical state of phospholipid molecules in the liposomes and the binding of fatty acid to FABP, suggesting that fatty acid must first desorb from the liposomes before FABP can have an effect. An FABP-fatty acid complex incubated with microsomes, in the absence of liposomes, resulted in greater acyl-CoA formation than when liposomes were present, suggesting that desorption of fatty acid from the membrane is rate-limiting in the accumulation of acyl-CoA by this system. Finally, an equilibrium dialysis cell separating liposomes from microsomes on opposite sides of a Nuclepore filter was used to show that liver FABP was required for the movement and activation of fatty acid between the compartments. These studies show that liver FABP interacts with fatty acid that desorbs from phospholipid bilayers, and promotes movement to a membrane-bound enzyme, suggesting that FABP may act intracellularly by increasing net desorption of fatty acid from cell membranes.

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