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Brain colchicine‐binding protein (tubulin) during postnatal development in the rat

A time‐decay colchicine‐binding assay was used under optimal conditions for measuring tubulin concentration in the cerebral cortex and cerebellum during postnatal development. In both brain areas soluble tubulin concentration (pmoles colchicine bound/mg tissue) declined by about 35% between 4 and 12 days of age after which the decrease was more gradual up to adulthood. Colchicine‐binding protein concentration of particulate fractions, on the other hand, increased between 4 and 12 days of age followed by relatively little change. The concentration of tubulin the soluble and particulate fractions of the cerebral cortex was 45% and 75% greater, respectively, than corresponding fractions of the cerebellum. The expression of tubulin on the basis of DNA, revealed marked regional differences which can be considered a reflection of differences in the relative extent of morphological differentiation in these areas during the postnatal period. Tubulin in both soluble and particulate fractions exhibited a marked increase in lability for colchicine binding from approximately 12 days of age. The half‐life for loss of colchicine‐binding activity was 2.5‐fold greater in particulate colchicine‐binding reaction provides additional support for the hypothesis that it represents a functionally significant association of tubulin with membranous components.