The biosynthesis by brain microsomes of cerebrosides containing nonhydroxy fatty acids

Abstract

Incubation of microsomes from mouse brain with UDP-gal, a long-chain base, and W-fatty acyl-CoA resulted in formation of NFA-cerebroside labeled in the fatty acid residue. The rate of synthesis was ten times that of the system lacking UDP-gal or long chain base. The incubation system also formed NFA-ceramide, at a much higher rate. Stearoyl-and lignoceroyl-CoA were much more effective in forming ceramide and cerebroside than palmitoyl-and oleoyl-CoA, a correlation which suggests that ceramide is an intermediate in cerebroside biosynthesis. When NFA-ceramide, together with a phospholipid mixture, was incubated wit,h labeled UDP-gal, NFA-cerebroside was formed. Utilization of the exogenous ceramide was demonstrated by a number of chromatographic procedures. Under the same conditions, but with labeled UDP-glc, the corresponding glucose-containing cerebroside was formed, at a somewhat higher rate. The organic synthesis of labeled lignoceric acid and lignoceroyl n-sphingosine is described. Also described is a simplified method for large-scale preparation of purified n-sphingosine. The labeled ceramide was utilized by the microsomes for the formation of galactosyl lignoceroyl sphingosine. Under a variety of conditions the microsomes failed to convert psychosine and labeled acyl-CoA-to cerebroside.

Reconstitution of ATP- and Cytosol-dependent Transport of de Novo Synthesized Ceramide to the Site of Sphingomyelin Synthesis in Semi-intact Cells

“…These reactions are catalyzed by ER-embedded enzymes, the catalytic sites of which face the cytosol (18 -20). Because the dihydrosphingosine-N-acyltransferase enzyme catalyzes acylation of sphingosine as well as dihydrosphingosine (21), production of Cer from sphingosine at the ER occurs under sphingosine-supplied conditions. In addition, conversion of metabolically labeled Cer to SM in intact cells can be blocked at low temperatures (22).…”

UDP‐Galactose Hydrolysis in Brain and Its Effect on Cerebroside Synthesis

“…They are synthesized in vitro mainly by a microsomal preparation from brain by the transfer of galactose from UDP-Gal to ceramide. Although this conversion has been studied in microsomes (Morell and Radin, 1969;Morell et al, 1970;Basu et al, 1971;Costantino-Ceccarini and Suzuki, 19751;Neskovic et al, 1976) as well as in myelin (Costantino-Ceccarini and Suzuki, 197%) and axolemma (Costantino-Ceccarini et al, 1979), the effect of the hydrolysis of UDP-Gal on the synthesis of cerebrosides has not been studied.…”

Synthesis and turnover of cerebrosides and phosphatidylserine of myelin and microsomal fractions of adult and developing rat brain

“…It is generally accepted that the enzymes that catalyse the synthesis of complex lipids are not present in myelin. Various reports have indicated that in the system in vitro, cerebrosides are mainly synthesized by the microsomal fraction of the brain (Morell et al, 1970;Neskovic et al, 1973;Shah, 1971). However, reports have appeared that indicate that there is some synthesis in vitro by the myelin (Neskovic et al, 1973;Constantino-Ceccarini & Suzuki, 1975;Chou & Jungalwala, 1976).…”

“…In view of these conflicting results, we have reinvestigated the problem of the turnover of cerebrosides in purified myelin in the adult and developing rat brain. Cerebrosides are mainly synthesized in the endoplasmic reticulum (microsomal fraction) (Morell et al, 1970). The turnover of cerebrosides in microsomal fractions was also determined simultaneously for comparison.…”