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BIOSYNTHESIS OF CHOLEST‐5‐ENE‐3β, 24‐DIOL (CEREBROSTEROL) BY BOVINE CEREBRAL CORTICAL MICROSOMES 1

The presence of cholest‐5‐ene‐3β, 24‐diol (cerebrosterol) in samples of human, bovine, and rabbit brains has been established by isolation of the sterol therefrom and identification by comparison of physical properties. Cholest‐5‐ene‐3β, 24‐diol was present at the level of 66.5 sg/g of dried tissue in human brain, 42.9 μg/g in cattle brain, and 89.5 pg/g in rabbit brain. Cholest‐5‐ene‐3β, 24‐diol was the only readily detectable hydroxycholesterol derivative in these brain tissues and was concentrated in the 105,000 g pellet (microsomal fraction) of both human and bovine cerebral cortex, with no demonstrable amounts of the sterol present in nuclear or mitochondrial fractions. Incubation of [1,2‐3H]‐ or of [4‐14C]‐cholesterol with the 105,000 g microsomal pellet from bovine cerebral cortical homogenates demonstrated 0.1‐0.38 per cent conversions to radioactive cholest‐5‐ene‐3β, 24‐diol, isolated and purified as the 3β, 24‐dibenzoate. The bioconversion required oxygen, and a stimulation of hydroxylation by added NADPH2 was demonstrated. Our observations establish that a sterol 24‐hydroxylase system is present in bovine cerebral cortex.