Kinetics of the interaction of a 41-kilodalton macrophage capping protein with actin: promotion of nucleation during prolongation of the lag period

A 41-kilodalton macrophage capping protein (MCP) has been isolated which is capable of forming complexes with actin monomers in addition to capping the barbed ends of actin filaments (Southwick & DiNubile, 1986). The protein is calcium activated in a fully reversible manner. Using kinetic assays...

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Bibliographic Details
Published in:Biochemistry (Easton) 1990-03, Vol.29 (9), p.2232-2240
Main Authors: Young, Clarence L, Southwick, Frederick S, Weber, Annemarie
Format: Article
Language:English
Subjects:
Acrosome - metabolism
actin
Actin Cytoskeleton - metabolism
Actin Depolymerizing Factors
Actins - metabolism
Analytical, structural and metabolic biochemistry
Animals
Binding and carrier proteins
Biological and medical sciences
Calcium - pharmacology
Cytoskeleton - metabolism
Destrin
Fluorescence
Fundamental and applied biological sciences. Psychology
Horseshoe Crabs
Kinetics
Macrophages - metabolism
Male
Microfilament Proteins - metabolism
Polymers
Proteins
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Summary:A 41-kilodalton macrophage capping protein (MCP) has been isolated which is capable of forming complexes with actin monomers in addition to capping the barbed ends of actin filaments (Southwick & DiNubile, 1986). The protein is calcium activated in a fully reversible manner. Using kinetic assays, we determined a capping constant, defined here as a modified Kd, of 1 nM and a Kd of 3-4 microM for MCP-actin monomer complex formation. MCP weakly nucleates actin polymerization: more than 0.5 microM MCP is necessary to shorten the lag period, and 1 microM MCP at an actin/MCP ratio of 10 reduces the average length of actin filaments to about 200 molecules per filament. We determined that the actin nucleus that survives MCP inactivation contains a minimum number of five actin molecules. These experiments also make a point with respect to the interpretation of the prolongation of the lag period. We directly demonstrate that in the presence of an actin binding protein a prolongation of the lag period can be associated with increased nucleation, contrary to the usual interpretation in the literature that it indicates no or decreased nucleation by the actin binding protein.
ISSN:0006-2960
1520-4995
DOI:10.1021/bi00461a005