Differential labelling of sphingolipids by [H-3]serine and ([H-3]methyl)-methionine in fish leukocytes

Long chain bases are constituents of all sphingolipids and their biosynthes is is presumed to occur via the initial condensation of serine with palmito yl-CoA. The biosynthesis of phytosphingosine, a long chain base containing three hydroxyl groups, has been less studied than sphingosine but is assume d to occur by hydroxylation of sphinganine. We report in this paper that th e label from ([H-3]methyl)-methionine is preferentially incorporated into p hytosphingosine bases of neutral glycosphingolipids, whereas the label from [H-3]serine is mainly incorporated into the sphingoid base of sphingomyeli n. These results show that in fish leukocytes the biosynthesis of individua l sphingoid bases and their downstream sphingolipid products follow differe nt pathways of metabolism. Our observations suggest that in fish leukocytes the synthesis of the constitutive long chain bases of sphingomyelin and co mplex glycosphingolipids is coordinately regulated and may be localized in separate compartments. (C) 2000 Elsevier Science Inc. All rights reserved.