PHYTOSPHINGOSINE BIOSYNTHESIS DIFFERS FROM SPHINGOSINE IN FISH LEUKOCYTES AND INVOLVES A TRANSFER OF METHYL-GROUPS FROM [H-3-METHYL] METHIONINE PRECURSOR

We have studied the incorporation of radioactivity from either [3-H-3] serine as the direct or [H-3-methyl]methionine as the indirect precurs or into sphingoid bases of free ceramides in lymphocytes from fish. Ra dioactivity from serine was incorporated mostly in the sphingosine moi ety of ceramides, In contrast, the radioactivity from methionine was e xclusively incorporated into phytosphingosine base (i.e., 4-hydroxy-sp hinganine) and the incorporation increased by about twofold in the pre sence of folic acid or niacinamide, Identity of the long-chain bases, phytosphingosine and sphingosine, was established chemically by thin-l ayer chromatography, chemical degradation, and gas-liquid chromatograp hy. (C) 1998 Academic Press.