Perez-Ramirez B, Shearwin KE, Timasheff SN. The colchicine-induced GTPase activity of tubulin: state of the product. Activation by microtubule-promoting cosolvents.
Biochemistry 1994;
33:6253-61. [PMID:
8193140 DOI:
10.1021/bi00186a027]
[Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Colchicine induces a weak assembly-independent GTPase activity in calf brain tubulin [David-Pfeuty, T., Erickson, H. P., & Pantaloni, D. (1977) Proc. Natl. Acad. Sci. U.S.A. 74, 5372-5376; Andreu, J. M., & Timasheff, S. N. (1981) Arch. Biochem. Biophys. 211, 151-157]. Kinetic analysis shows a turnover number of 2 x 10(-4) s-1 in 0.01 M sodium phosphate and 4 mM MgCl2, pH 7.0, with an apparent Km for GTP of 10 microM. This activity, which requires Mg2+ ions and attains a plateau at 4 mM MgCl2, is independent of pH over the pH range of 6.6-7.4. This GTPase activity was induced by all colchicine analogues that contain rings A and C (or C'), the strength varying in a manner parallel to the free energy of binding of the ligand. The specific GTPase activity was found to be independent of the tubulin-colchicine complex concentration over the range of 2-20 microM. Sedimentation velocity examination of the product of the reaction showed that GDP-tubulin-colchicine generated by hydrolysis of the E-site GTP was indistinguishable from that produced by nucleotide exchange at the site, the protein assuming the "curved" conformation in both cases. Steady-state kinetic analysis in the presence of high concentrations of microtubule-inducing cosolvent additives revealed an increase in kcat/Km of up to 1 order of magnitude that followed the order poly(ethylene glycol) 6000 (PEG-6000 > PEG-1000 = 2-methyl-2,4- pentanediol > sucrose > L-glutamate > glycerol = PEG-200 > betaine, with no apparent change in Km.(ABSTRACT TRUNCATED AT 250 WORDS)
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