Thiamine as an integral component of brain synaptosomal membranes.

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Abstract
Synaptic plasma membranes were prepared from rat cerebral cortex to determine if thiamin was localized in the membranes. The synaptosomes, prepared by discontinuous sucrose gradient centrifugation, were subjected to osmotic shock at pH 9.5 for 10-15 min and subfractionated on a discontinuous sucrose gradient. The 2 membrane fractions that were obtained were free of contamination by mitochondrial membrane and soluble fractions. To ensure specificity, thiamin was assayed fluorometrically before and after the addition of thiaminase I (thiamin:base 2-methyl-4-aminopyrimidine-5-methenyltransferase, EC 2.5.1.2). Thiamin content of the 2 membrane fractions was 9 and 10 pmol/mg protein.