The distribution of [14C]‐labeIled material into subcellular fractions of 15‐day‐old rat brain was studied as a function of time after intracerebral injection of [2‐14C]mevalonic acid. As previously shown for adult brain, the data indicated the microsomal fraction to be the site of sterol biosynthesis. The synaptosomal fraction exhibited a marked early uptake of [14C]‐nonsaponifiable material. Total radioactivity in both myelin and myelin‐like fractions remained low in comparison to that in the other subcellular fractions at all time periods examined. At 2 h after injection, labelled digitonin‐precipitable material was demonstrable in all subcellular fractions. Examination of the [14C]‐labelled nonsaponifiable material by thin‐layer chromatography indicated the rapid appearance of labelled 4‐desmethyl sterol in all subcellular fractions, with the most rapid appearance in the myelin fraction, followed in decreasing order by microsomal, synaptosomal, and mitochondrial fractions. Examination of [14C] digitonin‐precipitable material from each fraction by the dibromide method demonstrated that although 4‐desmethyl sterol appeared quickly, the formation of cholesterol was slow in all fractions, an effect that had been reported earlier for adult brain.
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Ramsey et al. (1972) studied this question.
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