J. Biol. Chem., Vol. 265, Issue 19, 11014-11016, Jul, 1990
Export of mitochondrially synthesized lysophosphatidic acid
D Haldar and L Lipfert
Department of Biological Sciences, St. John's University, Jamaica, New York 11439.
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.