title: Influence of mitochondria on phospholipid synthesis in preparations from rat liver.
abstract: 1. The addition of mitochondria to an incubation system containing the soluble and microsomal fractions of rat liver enhances severalfold the incorporation of each of ethanolamine, phosphorylethanolamine and CDP-ethanolamine into phosphatidylethanolamine. 2. In the presence of microsomal, mitochondrial and soluble fractions, CDP-ethanolamine exhibits the greatest initial rate of incorporation (approx. 6nmol/h per mg of protein), being slightly faster than that of phosphorylethanolamine (approx. 5nmol/h per mg of protein). Incorporation of ethanolamine proceeds very slowly for the first 20min and only after 30min gives rates approaching those of the other two precursors. 3. By using a substrate ;dilution' technique it was shown that in the reconstituted system the affinity of each of the enzymes for their respective substrates is very high: 10mum for ethanolamine, 25mum for phosphorylethanolamine and 5mum for CDP-ethanolamine. 4. Isolation of the mitochondrial and microsomal fractions from the medium after incubation together with phosphorylethanolamine showed that about 70% of the total radioactivity was present in the microsomal fraction and about 30% in the mitochondria after only 20min. Similar experiments with ethanolamine as precursor revealed that after 20min only about 15% of the total radioactivity was present in the mitochondria but that after 40min about 30% was present in this fraction. 5. Heating and phospholipase treatment of mitochondria, but not freeze-thawing, eliminated the stimulatory effect of mitochondria on phospholipid synthesis. 6. The reconstituted system exhibits an absolute requirement for Mg(2+) (2mm gave maximal rates) and is inhibited by very low concentrations of Ca(2+) (100mum-Ca(2+) produced half-maximal inhibition with 3mm-Mg(2+)). Further addition of Mg(2+) overcame the Ca(2+) inhibition, suggesting that the inhibitory effect is readily reversible. 7. The concept that modification of the Mg(2+)/Ca(2+) ratio is a means of controlling the rate of cellular phospholipid synthesis is introduced.
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002250:Carbon Radioisotopes; D003597:Cytosine Nucleotides / Q000378:metabolism; D003576:Electron Transport Complex IV / Q000032:analysis; D004983:Ethanolamines / Q000378:metabolism; D005952:Glucose-6-Phosphatase / Q000032:analysis; D066298:In Vitro Techniques; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D008862:Microsomes, Liver / Q000378:metabolism; D008930:Mitochondria, Liver / Q000378:metabolism*; D010714:Phosphatidylethanolamines / Q000096:biosynthesis*; D051381:Rats; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D002250:Carbon Radioisotopes; D003597:Cytosine Nucleotides; D004983:Ethanolamines; D010714:Phosphatidylethanolamines; D003576:Electron Transport Complex IV; D005952:Glucose-6-Phosphatase; D008274:Magnesium; D002118:Calcium