@article{c64029c309244f4fb836beaa9f15b46e,
title = "Rings are not microtubule assembly intermediates: An analysis of the lag phase in GTP-dependent self-assembly of bovine brain tubulin",
abstract = "The assembly of whole microtubule protein, derived from bovine brain extracts by multiple cycles of temperature-induced assembly and disassembly, exhibits a lag phase in which there is a characteristic, transient drop in the turbidity. This drop is inconsistent with the direct participation of ring-like structures in microtubule assembly, and warming microtubule protein in the presence of GDP unmasks the kinetics of this dissociation phenomenon. These and other data suggest that rings are enthalpy-stabilized and are unlikely intermediates in the entropy-driven self-assembly of microtubules.",
author = "Karr, {Timothy L.} and Purich, {Daniel L.}",
note = "Funding Information: The dynamics of reversible entropy-driven polymer formation has been considered as occurring in four separate phases of the condensation equilibrium model of Oosawa and Kasai (i) : nucleation) elongation) attainment of a polymer-protomer equilibrium; and final polymer length redistribution from a kinetically to an equilibrium controlled system. The nucleation process is a fleeting event, and its characterization has been most challenging. Several investigators (2-4) have sought to unify the formation of ring-like structures with the early self-assembly reactions involved in nucleation to provide a logical basis for in vitro ring formation. Rings are cold-stable structural elements created during cold-depolymerization of microtubules (5,6), and they have been attractive as possible assembly intermediates because they are well defined, highly organized tubulin-containing structures. Yet, the closed structure of rings has a diameter in excess of that of a microtubule (6), and one must consider the possibility that the ring-structures might open to form protofilaments as an essential step in tubule assembly. Another possibility is that the ring-like structures are abortive association complexes which form during cold-depolymerization by formation of new interprotomeric bonds of greater enthalpic stability. If so, these structures may only appear to be precursors of microtubules by virtue of their service as a depot for tubulin and microtubule associated proteins. In this case, self- *This research was supported in part by NIH Research Grant GM-24958 and Biomedical Research Support Grant RR-07099. +Earle C. Anthony Graduate Research Fellow, University of California. tRecipient of an NIH Research Career Development Award and an Alfred P. Sloan Foundation Fellowship. Copyright: Copyright 2017 Elsevier B.V., All rights reserved.",
year = "1980",
doi = "10.1016/S0006-291X(80)80119-7",
language = "English (US)",
volume = "95",
pages = "1885--1889",
journal = "Topics in Catalysis",
number = "4",
}