CHOLINE BASE EXCHANGE ACTIVITY IN RAT HEPATOCYTE NUCLEI AND NUCLEAR MEMBRANES |
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| Authors: | E ALBI MP VIOLA-MAGNI |
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| Institution: | 1. Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA;2. Laboratory of Cell and Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA;3. Department of Cellular and Molecular Pharmacology, University of California at San Francisco, San Francisco, CA 94158, USA;4. Howard Hughes Medical Institute, University of California at San Francisco, San Francisco, CA 94158, USA;5. Calico Life Sciences LLC, South San Francisco, CA 94080, USA;1. Stanford Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA 94305, USA;2. Department of Medicine, Division of Cardiovascular Medicine, Stanford University School of Medicine, Stanford, CA 94305, USA;3. Greenstone Biosciences, Palo Alto, CA, 94304, USA |
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| Abstract: | Previous investigations have demonstrated the presence of phospholipids as a component of chromatin; however the mechanism of their synthesis, namely if they are synthesized in the nuclei or in the cytoplasm (microsomal fraction), from where they may eventually be transported to the nucleus, has not yet been clarified. The phosphatidylcholine, for example, can be formed, albeit in a limited amount, by an interconversion reaction between bases. The aim of the present research was to ascertain the presence of the enzyme complex responsible for this reaction in hepatocyte nuclei and in isolated nuclear membrane. The incorporation of 14C]-choline in phosphatidylcholine was assayed in microsomes, hepatocyte nuclei, liver nuclei and nuclear membranes of rat liver. The reaction was Ca2+-dependent and the specific activity was higher in microsomes but was present, albeit at a low level, also in nuclei and in nuclear membranes. Possible contaminations were excluded by specific microsomal markers and by the reaction time course. In fact, the nuclear reaction reached the maximum level slowly with respect to microsomes. Since the phosphatidylcholine extracted from the nuclei show an enrichment in unsaturated fatty acids of monoenoic fraction, such as oleic acid, the difference in reaction kinetics has been tentatively explained as due to the phosphatidylcholine fatty acid content. The presence of this base exchange enzyme complex may allow a fast change in chromatin phospholipid composition. |
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| Keywords: | choline base exchange hepatocyte nuclei nuclear membranes |
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