Metabolism of cerebrosides and sulfatides in the nervous system of Xenopus tadpole during metamorphosis.

Xenopus laevis tadpoles undergoing metamorphosis were used to study the turnover of cerebrosides and sulfatides in the nervous system of the frog. Tadpoles at the beginning of metamorphosis were treated by intraperitoneal injection with [U-14C]glucose and radioactivity incorporated into galactosphingolipids of brain and tail was measured after various times. The specific activity of brain cerebrosides increased rapidly for the first 24 hr after injection, reached a plateau after 48 hr, and then declined 40% by 7 days. The specific activity of sulfatides changed somewhat more slowly. Hydroxy fatty acid-containing galactosphingolipids had nearly twice the specific activity compared with their nonhydroxy counterparts in brain. Despite the complete regression of tail nerve cord, metabolism of glycosphingolipids in this tissue also indicated active synthesis as well as degradation during this period. The specific activities of these lipids were similar and all reached a peak 24 hr after injection. Examination of the components of these galactosphingolipids disclosed that only a small fraction (7-25%) of the radioactivity was in the galactose moiety in both brain and tail. The ratios of the radioactivity in fatty acid to that in the sphingoid base were much higher for hydroxycerebroside and hydroxysulfatide than for the nonhydroxy isomers.