ISSN:
0091-7419
Keywords:
Life Sciences
;
Molecular Cell Biology
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
Notes:
Microtubule polymerization in vitro was examined using material purified from porcine brain tissue by a reversible temperature dependent assembly procedure, and was characterized by electron microscopy, viscometry, and sedimentation. The reaction was endothermic, colchicine sensitive, and occurred at neutral pH and moderate ionic strength. Divalent cations (calcium, magnesium) were inhibitory at millimolar concentrations, but stimulated polymerization at the micromolar level. Nucleoside triphosphates were required for assembly of purified subunits. As determined by quantitative sedimentation analyses, the reaction was an equilibrium process. Below a critical concentration of tubulin no assembly occurred. Analytical ultracentrifugation studies indicated that tubulin species with sO20, w of 6S and 30S were in equilibrium with each other, and that both were incorporated into microtubules. Electron microscopic analyses suggested that disc (or ring) structures might be intermediates in assembly, and that they were primarily utilized early in the polymerization process. Assembly could be seeded by mixing microtubular fragments from brain or flagella with brain microtubule subunits; depending on conditions of temperature and protein concentration, addition of subunits occurred either with unipolar or biased polar directionality. The possible significance of these properties of the polymerization reaction for control of assembly is discussed.
Additional Material:
12 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jss.400020230
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