Characterization of microtubule-associated proteins isolated from bovine adrenal gland

We investigated the biochemical characteristics of microtubule-associated proteins (MAPs) of both the adrenal medulla and the cortex. The major constituents of the adrenal MAPs isolated by the taxol-dependent procedure [Vallee, R. B. (1982) J. Cell. Biol. 92, 435-442] were several polypeptides in the high-molecular-mass region (high-Mr MAPs) and a 190000-Mr polypeptide (190-kDa MAP). In the cortex MAP fraction, the most prominent component was 190-kDa MAP, while the medulla MAP fraction was rich in high-Mr MAPs. Twice-cycled microtubule proteins prepared without taxol from the same sources also contained high-Mr MAPs and 190-kDa MAP. High-Mr MAPs contained protein species identical to MAP1 and MAP2 of mammalian brain as judged from electrophoretic mobility, heat-stability and immunoreactivity. 190-kDa MAP was classified as MAP subspecies distinct from high-Mr MAPs by several criteria. The MAP fractions had the ability to polymerize purified tubulin into microtubules, and the major MAP species (high-Mr MAPs and 190-kDa MAP) were found to cosediment with reconstituted microtubules. Tau factor, one of the major MAPs in the mammalian brain, appeared to be a minor species in the adrenal gland.