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T L Karr

Publications and source records attributed to T L Karr.

48 records · Page 3Linked to original sources
PubMed1980

Calcium ion induces endwise depolymerization of bovine brain microtubules.

Calcium ion induces rapid depolymerization of microtubules, and the mechanism of interaction of Ca2+ with cytoskeletal components may be metabolically significant. The sufficiency of an endwise depolymerization model for describing calcium-induced disassembly was demonstrated by three criteria: (a) correlation of the observed time course of disassembly with the initial polymer length distribution using a kinetic model described elsewhere (Kristofferson, D., Karr, T. L., and Purich, D. L. (1980) J. Biol. Chem. 255, 8567-8572); (b) observation that the initial rate of calcium-induced disassembly parallels the microtubule number of concentration which is experimentally manipulated by mechanical shearing; and (c) determination of the average polymer length, microtubule number concentration, and extent of depolymerization at various levels of added calcium ion to achieve successive partial disassembly extents. The rate constant for protomer release and other aspects of the disassembly mechanisms are also presented. Critical concentration measurements at low calcium ion levels are also consistent with endwise interactions.

Animals↗
PubMed1980

Dynamics of linear protein polymer disassembly.

This report presents a kinetic model for endwise depolymerization of linear, self-assembling protein systems. We develop a reliable method for predicting the shape of depolymerization curves (remaining polymer weight versus time) on the basis of the initial polymer length distribution. Computer simulations are used to illustrate changes in the polymer length distribution and average polymer weight during disassembly. In addition, our method provides an accurate determination of the microscopic rate constant for subunit release. Application of this analysis to dilution-induced and cold induced disassembly of microtubules is illustrated in the preceding paper (Karr, T.L., Kristofferson, D., and Purich, D.L. (1980) J. Biol. Chem. 255, 8560-8566). A survey of other possible applications of this treatment to microtubules, flagella, F-actin, and tobacco mosaic virus protein is included.

Actins↗
PubMed1980

Mechanism of microtubule depolymerization. Correlation of rapid induced disassembly experiments with a kinetic model for endwise depolymerization.

Microtubule disassembly has been studied using a rapid dilution technique (Karr, T.L., and Purich, D.L. (1979) J. Biol. Chem. 254, 10885-10888). Disassembly curves, generated by computer from the solution of series first order differential equations (see following paper), were fit to experimental data with excellent agreement when the diluted microtubules contained no microtubule-associated proteins. The rate constant for dimer release from microtubules was found to be 154 s-1. Assuming a critical tubulin concentration of 8 to 9 x 10(-6) M, the apparent bimolecular rate constant (2 x 10(7) M-1 s-1) for assembly is near the diffusion limit. It was also possible to use the rapid dilution technique for quantitatively correlating the disassembly rate to the number concentration of microtubule ends. These findings suggest that the dynamics of tubulin interactions with microtubules may be characterized in terms of an endwise depolymerization model. A re-evaluation of cold induced depolymerization kinetics (see miniprint supplement) is also fully consistent with our analysis of disassembly dynamics.

Kinetics↗
PubMed1979

Participation of guanine nucleotides in nucleation and elongation steps of microtubule assembly.

Critical concentrations for formation of microtubules from subunits with GTP and its beta, gamma-imido and beta, gamma-methylene analogs are similar when adequate time is given for equilibration. Dilution of microtubules into GTP and GDP yielded values of 0.1 and 0.19 mg/ml for the critical concentration, results similar to those reported by Carlier and Pantaloni [Carlier, M. & Pantaloni, D. (1978) Biochemistry 17, 1908-1915]. GDP is capable of supporting elongation of preformed microtubules, but it efficiently poisons the nucleation events. Reported experiments also demonstrate that the critical tubulin concentration of the tubulin-GDP complex can be accurately measured in both the assembly and disassembly directions. Evidence is presented that GTP is involved in early nucleation events but that microtubules are stabilized in the presence of either GTP or GDP. These results are discussed in terms of a condensation-equilibrium model in which tubulin subunits equilibrate rapidly with microtubule ends, and their affinity for the ends is governed by the nucleotide ligand at the exchangeable site.

Animals↗