Microtubules subunit lattices

Tubulin is a dimer composed of similar but not identical polypeptides, a and )8, one of which (a) is phosphorylated. The molecular weight of tubulin is 100,000, with each of the subunits having a molecular weight of 55,000. Tubulin polymerizes, forming a polar, helical surface lattice. Microtubules are stabilized by Mg + and GTP, which also promote the polymerization. Ca " inhibits polymerization and may promote depolymerization (Weisenberg, 1972 Staprans et al., 1975). Brain tubulin is phosphorylated, possibly by cAMP-stimulated protein kinase, which is one of many microtubule-associated proteins. Colchicine blocks polymerization by binding to the growing end of a micro-... 

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