Cells in culture often undergo a 'burst' of free sphingosine, sphingosine 1-phosphate, ceramide, and other bioactive lipids upon removal of 'conditioned' medium, and at least one lipid signaling pathway (protein kinase C) has been shown to be affected by these changes (Smith, E. R. and Merrill A. H., Jr. (1995) J. Biol. Chem. 270, 18749-18758; Smith, E. R., Jones, P. L., Boss, J. M. and Merrill, A. H., Jr. (1997) J. Biol. Chem. 272, 5640-5646). Whereas increases in sphinganine and dihydroceramide are responses to provision of precursors for sphingolipid biosynthesis de novo in the new medium, the sphingosine burst is due to sphingolipid turnover upon removal of suppressive factor(s) in conditioned medium. This study describes the purification and characterization of these suppressive factors. Conditioned medium from J774 cells was fractionated into two components that suppress the burst as follows: ammonium ion, which reaches 2-3 mM within 48 h of cell culture; and a low molecular weight, cationic compound that has been assigned the structure 2,6-bis(ω-aminobutyl)-3,5-diimino-piperazine (for which we suggest the name 'batrachamine' based on its appearance) by 1H and 13C NMR, Fourier transform infrared spectroscopy, and mass spectrometric analyses. The physiological significance of these compounds as suppressors of sphingolipid metabolism is unclear; however, ammonium ion is a by-product of amino acid catabolism and reaches high concentrations in some tissues. Batrachamine is even more intriguing because this is, as far as we are aware, the first report of a naturally occurring compound of this structural type. Considering the many cell functions that are affected by sphingoid bases and their derivatives, the effects of NH4 and batrachamine on sphingolipid metabolism may have important implications for cell regulation.
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