OBSERVATIONS ON THE BIOSYNTHESIS OF RAT BRAIN CERAMIDE AND CEREBROSIDE IN VIVO

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Abstract
Abstract— The incorporation in vivo of l‐[14C]serine into ceramide and cerebroside of young rat brain has been studied. Acid hydrolysis of labelled ceramide and galactosyl‐ceramide followed by selective partitioning of the resulting components indicated that 88 per cent of the radioactivity was present in the long‐chain base portion. At early time points (10 min, 20 min) the precursor was incorporated into ceramide and to a lesser degree into glucosyl‐ceramide. During time intervals of 5 and 10 h, the specific activity values (d.p.m./μmol) for ceramide and glucosyl‐ceramide decreased, while values for galactosyl‐ceramide, containing either unsubstituted fatty acids (NFA) or α‐hydroxy fatty acids (HFA), increased 50 and 30 per cent, respectively. Analysis of labelled ceramide at all time points studied (10 min‐10 h) indicated that l‐[14C]serine was incorporated onto the NFA type. This observation suggests that HFA‐ceramide may not be the physiological precursor of HFA‐galactosyl‐ceramide. In this context, the postulated precursor roles of both ceramide and psychosine in the biosynthesis of brain cerebrosides are discussed.

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