Abstract
The choline-deficient rat liver has been chosen as a physiologically relevant model system in which to study the regulation of phosphatidylcholine biosynthesis. When 50-g rats were placed on a choline-deficient diet for 3 days, the activity of CTP:phosphocholine cytidylyltransferase (CT) was increased 2-fold in the microsomes and decreased proportionately in the cytosol. A low titer antibody to CT was obtained from chickens and used to identify the amount of CT protein in cytosol from rat liver. The amount of CT recovered from the choline-deficient cytosol was significantly less than in cytosol from choline-supplemented rats. When hepatocytes were prepared from choline-deficient livers, supplementation of the medium of the cells with choline caused CT to move from the membranes to cytosol within 1-2 h. The activity of another translocatable enzyme of glycerolipid metabolism, phosphatidate phosphohydrolase, was unchanged in cytosol from choline-deficient rat livers, and the microsomal activity of this enzyme was only minimally increased. When the livers were fractionated into endoplasmic reticulum and Golgi, there was a 2-fold increase in the activity on the endoplasmic reticulum from choline-deficient livers but no change in activity associated with Golgi. Thus, the increased association of CT with endoplasmic reticulum in choline-deficient livers appears to be specific to that subcellular fraction, and the subcellular location of other enzymes may not be affected.
Highlights
The choline-deficient rat liver has been chosen as a physiologically relevant model system in which to study the regulation of phosphatidylcholine biosynthesis
Weinhold et al [21] showed a correlation between the levels of fatty acids in lung after birth and the CT activity bound to membranes as well as the rate of PC biosynthesis
In the past few years two studies have been published on the effect of choline deficiency on PC biosynthesis in cultured animal cells, An increase in the microsomal activity of cytidylyltransferase and a concomitant decrease in the cytosolic activity of the enzyme have been observed in type II pneumonocytes [31], LM cells, and Chinese hamster ovary cells [32]
Summary
~drnonta~, Alberta T6G 252, Canada of 3~a~~rn~t~, Universi~ of A~rtu, Downloaded from http://www.jbc.org/ by guest on October 7, 2020. In the past few years two studies have been published on the effect of choline deficiency on PC biosynthesis in cultured animal cells, An increase in the microsomal activity of cytidylyltransferase and a concomitant decrease in the cytosolic activity of the enzyme have been observed in type II pneumonocytes [31], LM cells, and Chinese hamster ovary cells [32]. As DG has been shown to cause CT to bind to membranes (lo), an increase in this lipid would be an plausible mechanism for mediating CT translocation in choline-deficient cells. The effect appears to be very specific for CT since another enzyme, phosphatidate phosphohydrolase, known to be translocated under many of the same conditions that enhances CT binding to membranes, was only marginally affected in the choline-deficient livers
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