Skip to main content
NCBI home page
Biochemical Journal logoLink to Biochemical Journal
. 1988 Dec 15;256(3):821–828. doi: 10.1042/bj2560821

Rat and human mammary tissue can synthesize choline moiety via the methylation of phosphatidylethanolamine.

E K Yang 1, J K Blusztajn 1, E A Pomfret 1, S H Zeisel 1
PMCID: PMC1135489  PMID: 3223955

Abstract

The normal mammal requires large amounts of choline for maintenance and growth of tissue mass. Since milk, the only food for neonates, has many-fold higher free choline concentration than does maternal plasma, it is possible that mammary gland can synthesize choline molecules. The only known mammalian pathway for the synthesis de novo of choline molecules is catalysed by phosphatidylethanolamine N-methyltransferase (PeMT), which synthesizes phosphatidylcholine (PtdCho) via sequential methylation of phosphatidylethanolamine (PtdEtn) using S-adenosylmethionine (AdoMet) as a methyl donor. We identified PeMT activity in rat mammary tissue, and differences in affinities for substrate, as well as in activities as a function of pH, suggest that at least two distinct enzyme activities are involved [i.e. one catalysing the methylation of PtdEtn to form phosphatidyl-N-methylethanolamine (PtdMeEtn) and the other catalysing the methylation of PtdMeEtn and phosphatidyl-NN-dimethylethanolamine (PtdMe2Etn) to form PtdMe2Etn and PtdCho, respectively]. The relationships between AdoMet concentrations and PtdCho formation from endogenous PtdEtn in rat mammary homogenate were complex: a sigmoidal component (with a Hill coefficient of 2.2), requiring 55 microM-AdoMet for half saturation (Vmax. = 9 pmol/h per mg of protein), and a high affinity component (Kapparent = 8.7 microM and Vmax. = 3.8 pmol/h per mg of protein) were identified. When exogenous PtdMe2Etn was added as substrate, PtdCho formation exhibited Michaelis-Menten kinetics for AdoMet, and its affinity for AdoMet was high (Kapparent = 9 microM, Vmax. = 85 pmol/h per mg of protein). In the presence of endogenous substrates, the rates of PeMT-catalysed PtdCho formation within homogenates of rat mammary tissue were similar in tissue from lactating and non-lactating animals. When exogenous PtdMe2Etn was added to homogenates of rat mammary tissue, tissue from lactating rats made twice as much PtdCho as did tissue from non-lactating rats. Isolated mammary epithelial cells also exhibited PeMT activity; the rate of formation of PtdCho was much greater in intact versus broken cells. We also identified PeMT activity in homogenates of mammary tissue from non-lactating humans. The rate of PtdCho formation was of similar magnitude to that seen in rat tissue. This evidence supports the hypothesis that some of the choline found in milk could have been synthesized de novo in the mammary gland.

Full text

PDF
821

Images in this article

824Fig. 1.
on p.824
824Fig. 2.
on p.824
826Fig. 6.
on p.826
826Fig. 7.
on p.826

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Audubert F., Vance D. E. Pitfalls and problems in studies on the methylation of phosphatidylethanolamine. J Biol Chem. 1983 Sep 10;258(17):10695–10701. [PubMed] [Google Scholar]
  2. Bhattacharya A., Vonderhaar B. K. Phospholipid methylation stimulates lactogenic binding in mouse mammary gland membranes. Proc Natl Acad Sci U S A. 1979 Sep;76(9):4489–4492. doi: 10.1073/pnas.76.9.4489. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Bidlingmeyer B. A., Cohen S. A., Tarvin T. L. Rapid analysis of amino acids using pre-column derivatization. J Chromatogr. 1984 Dec 7;336(1):93–104. doi: 10.1016/s0378-4347(00)85133-6. [DOI] [PubMed] [Google Scholar]
  4. Blusztajn J. K., Wurtman R. J. Choline biosynthesis by a preparation enriched in synaptosomes from rat brain. Nature. 1981 Apr 2;290(5805):417–418. doi: 10.1038/290417a0. [DOI] [PubMed] [Google Scholar]
  5. Blusztajn J. K., Zeisel S. H., Wurtman R. J. Developmental changes in the activity of phosphatidylethanolamine N-methyltransferases in rat brain. Biochem J. 1985 Dec 1;232(2):505–511. doi: 10.1042/bj2320505. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Blusztajn J. K., Zeisel S. H., Wurtman R. J. Synthesis of lecithin (phosphatidylcholine) from phosphatidylethanolamine in bovine brain. Brain Res. 1979 Dec 28;179(2):319–327. doi: 10.1016/0006-8993(79)90447-5. [DOI] [PubMed] [Google Scholar]
  7. Bradford M. M. A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal Biochem. 1976 May 7;72:248–254. doi: 10.1016/0003-2697(76)90527-3. [DOI] [PubMed] [Google Scholar]
  8. Chao C. K., Pomfret E. A., Zeisel S. H. Uptake of choline by rat mammary-gland epithelial cells. Biochem J. 1988 Aug 15;254(1):33–38. doi: 10.1042/bj2540033. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Greenberg M. L., Klig L. S., Letts V. A., Loewy B. S., Henry S. A. Yeast mutant defective in phosphatidylcholine synthesis. J Bacteriol. 1983 Feb;153(2):791–799. doi: 10.1128/jb.153.2.791-799.1983. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Higgins J. A. Biogenesis of endoplasmic reticulum phosphatidylcholine. Translocation of intermediates across the membrane bilayer during methylation of phosphatidylethanolamine. Biochim Biophys Acta. 1981 Jan 8;640(1):1–15. doi: 10.1016/0005-2736(81)90527-7. [DOI] [PubMed] [Google Scholar]
  11. Hirata F., Axelrod J. Enzymatic methylation of phosphatidylethanolamine increases erythrocyte membrane fluidity. Nature. 1978 Sep 21;275(5677):219–220. doi: 10.1038/275219a0. [DOI] [PubMed] [Google Scholar]
  12. Hirata F., Axelrod J. Enzymatic synthesis and rapid translocation of phosphatidylcholine by two methyltransferases in erythrocyte membranes. Proc Natl Acad Sci U S A. 1978 May;75(5):2348–2352. doi: 10.1073/pnas.75.5.2348. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Hirata F., Axelrod J. Phospholipid methylation and biological signal transmission. Science. 1980 Sep 5;209(4461):1082–1090. doi: 10.1126/science.6157192. [DOI] [PubMed] [Google Scholar]
  14. Liscovitch M., Freese A., Blusztajn J. K., Wurtman R. J. High-performance liquid chromatography of water-soluble choline metabolites. Anal Biochem. 1985 Nov 15;151(1):182–187. doi: 10.1016/0003-2697(85)90069-7. [DOI] [PubMed] [Google Scholar]
  15. Newman R. A., Klein P. J., Rudland P. S. Binding of peanut lectin to breast epithelium, human carcinomas, and a cultured rat mammary stem cell: use of the lectin as a marker of mammary differentiation. J Natl Cancer Inst. 1979 Dec;63(6):1339–1346. [PubMed] [Google Scholar]
  16. Pajares M. A., Villalba M., Mato J. M. Purification of phospholipid methyltransferase from rat liver microsomal fraction. Biochem J. 1986 Aug 1;237(3):699–705. doi: 10.1042/bj2370699. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Ridgway N. D., Vance D. E. Purification of phosphatidylethanolamine N-methyltransferase from rat liver. J Biol Chem. 1987 Dec 15;262(35):17231–17239. [PubMed] [Google Scholar]
  18. Shivapurkar N., Poirier L. A. Tissue levels of S-adenosylmethionine and S-adenosylhomocysteine in rats fed methyl-deficient, amino acid-defined diets for one to five weeks. Carcinogenesis. 1983 Aug;4(8):1051–1057. doi: 10.1093/carcin/4.8.1051. [DOI] [PubMed] [Google Scholar]
  19. Threadgold L. C., Coore H. G., Kuhn N. J. Monosaccharide transport into lactating-rat mammary acini. Biochem J. 1982 May 15;204(2):493–501. doi: 10.1042/bj2040493. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Zeisel S. H., Char D., Sheard N. F. Choline, phosphatidylcholine and sphingomyelin in human and bovine milk and infant formulas. J Nutr. 1986 Jan;116(1):50–58. doi: 10.1093/jn/116.1.50. [DOI] [PubMed] [Google Scholar]
  21. Zeisel S. H. Dietary choline: biochemistry, physiology, and pharmacology. Annu Rev Nutr. 1981;1:95–121. doi: 10.1146/annurev.nu.01.070181.000523. [DOI] [PubMed] [Google Scholar]
  22. Zeisel S. H., Epstein M. F., Wurtman R. J. Elevated choline concentration in neonatal plasma. Life Sci. 1980 May 26;26(21):1827–1831. doi: 10.1016/0024-3205(80)90585-8. [DOI] [PubMed] [Google Scholar]
  23. Zeisel S. H., Wurtman R. J. Developmental changes in rat blood choline concentration. Biochem J. 1981 Sep 15;198(3):565–570. doi: 10.1042/bj1980565. [DOI] [PMC free article] [PubMed] [Google Scholar]

Articles from Biochemical Journal are provided here courtesy of The Biochemical Society

RESOURCES