Norris Andrew W, Spector Arthur A
Department of Pediatrics, University of Iowa College of Medicine, Iowa City, IA 52242, USA.
J Lipid Res. 2002 Apr;43(4):646-53.
Synthesis of n-3 and n-6 very long chain-PUFAs (VLC-PUFAs) from 18-carbon essential fatty acids is differentially regulated. The predominant product arising from n-3 fatty acids is docosahexaenoic acid (22:6n-3), with the liver serving as the main site of production. The synthetic pathway requires movement of a 24-carbon intermediate from the endoplasmic reticulum to peroxisomes for retroconversion to 22:6n-3. The mechanism of this intra-organelle flux is unknown, but could be binding-protein facilitated. We thus investigated binding of a series of previously untested VLC-PUFAs to liver fatty acid-binding protein (L-FABP). Three fluorometric assays were employed, all of which showed strong binding (K(d)' approximately 10(-8) to 10(-7) M) of 20-, 22-, and 24-carbon n-3 PUFAs to L-FABP. In contrast, synthesis of the predominant n-6 PUFA product, arachidonic acid, does not require intra-organelle transport. However, we found that n-6 VLC-PUFAs bound to L-FABP with affinities (K(d)' approximately 10(-8) to 10(-7) M) comparable to their n-3 counterparts. Although these results raise the possibility that L-FABP may participate in the cytoplasmic processing of n-3 and n-6 VLC-PUFAs, there is no evidence on the basis of binding affinities that L-FABP accounts for differences in the predominant products formed by the n-3 and n-6 PUFA metabolic pathways.
从18碳必需脂肪酸合成n-3和n-6超长链多不饱和脂肪酸（VLC-PUFAs）的过程受到不同的调控。n-3脂肪酸产生的主要产物是二十二碳六烯酸（22:6n-3），肝脏是主要的合成部位。合成途径需要一种24碳中间体从内质网转运到过氧化物酶体，以便逆向转化为22:6n-3。这种细胞器内通量的机制尚不清楚，但可能是由结合蛋白促进的。因此，我们研究了一系列先前未经测试的VLC-PUFAs与肝脏脂肪酸结合蛋白（L-FABP）的结合情况。采用了三种荧光测定法，所有这些方法都表明20碳、22碳和24碳的n-3多不饱和脂肪酸与L-FABP有很强的结合（解离常数K(d)'约为10^(-8)至10^(-7) M）。相比之下，主要的n-6多不饱和脂肪酸产物花生四烯酸的合成不需要细胞器内运输。然而，我们发现n-6 VLC-PUFAs与L-FABP的结合亲和力（K(d)'约为10^(-8)至10^(-7) M）与其n-3对应物相当。尽管这些结果增加了L-FABP可能参与n-3和n-6 VLC-PUFAs胞质加工的可能性，但基于结合亲和力，没有证据表明L-FABP解释了n-3和n-6多不饱和脂肪酸代谢途径形成的主要产物的差异。
