Haldar D, Lipfert L
Department of Biological Sciences, St. John's University, Jamaica, New York 11439.
J Biol Chem. 1990 Jul 5;265(19):11014-6.
We have previously demonstrated that the properties of mitochondrial glycerophosphate acyltransferase are in keeping with the asymmetric distribution of fatty acids found in naturally occurring cell glycerophospholipids. We are now examining if mitochondria can export lysophosphatidic acid and if it is converted to other phospholipids by the microsomes. Rat liver mitochondria were incubated for 3 min with [2-3H]-sn-glycerol 3-phosphate, palmityl-CoA, and N-ethylmaleimide in the acyltransferase assay medium. In the absence of bovine serum albumin in the medium, greater than 80% of the phospholipids sedimented with the mitochondria. In the presence of the albumin, the lysophosphatidic acid was present entirely in the supernatant fluid. The very little phosphatidic acid that was formed sedimented with the mitochondria. Addition of microsomes to the supernatant fluid followed by a further incubation of 5 min converted 61% of the lysophosphatidic acid to phosphatidic acid which sedimented with the microsomes. When mitochondria and microsomes were incubated together in the assay medium containing albumin and N-ethylmaleimide, the product contained more phosphatidic and less lysophosphatidic acid. When the subcellular components were reisolated by differential centrifugation, 70% of the phosphatidic acid sedimented with the microsomes and the lysophosphatidic acid stayed in the postmicrosomal supernatant. Thus, under appropriate conditions mitochondrially produced lysophosphatidic acid can leave the organelles and this phospholipid can be converted to phosphatidic acid by the microsomes.
我们之前已经证明，线粒体甘油磷酸酰基转移酶的特性与天然存在的细胞甘油磷脂中脂肪酸的不对称分布相符。我们现在正在研究线粒体是否能够输出溶血磷脂酸，以及它是否会被微粒体转化为其他磷脂。在酰基转移酶测定培养基中，将大鼠肝脏线粒体与[2-³H]-sn-甘油3-磷酸、棕榈酰辅酶A和N-乙基马来酰亚胺一起孵育3分钟。在培养基中不存在牛血清白蛋白的情况下，超过80%的磷脂与线粒体一起沉淀。在白蛋白存在的情况下，溶血磷脂酸完全存在于上清液中。形成的极少量磷脂酸与线粒体一起沉淀。向上清液中加入微粒体，再孵育5分钟后，61%的溶血磷脂酸转化为与微粒体一起沉淀的磷脂酸。当线粒体和微粒体在含有白蛋白和N-乙基马来酰亚胺的测定培养基中一起孵育时，产物中磷脂酸含量更多，溶血磷脂酸含量更少。当通过差速离心重新分离亚细胞成分时，70%的磷脂酸与微粒体一起沉淀，而溶血磷脂酸则留在微粒体后的上清液中。因此，在适当条件下，线粒体产生的溶血磷脂酸可以离开细胞器，并且这种磷脂可以被微粒体转化为磷脂酸。
