title: Kinetic studies on the effect of yeast cofilin on yeast actin polymerization.
abstract: The effect of yeast cofilin on the kinetics of polymerization of yeast actin has been examined at 20 degrees C at both pH 8.0 and 6.6. In the absence of cofilin, the kinetic data may be described by a simple nucleation-elongation mechanism. Kinetic data in the presence of cofilin suggests a complex dependence on the cofilin concentration. At low cofilin-to-actin ratios, cofilin increases the rate of polymerization in a way best fit by assuming filament fragmentation. The apparent fragmentation rate constants increase with increasing cofilin concentration leveling off above a cofilin-to-actin ratio of 1:8 and are independent of pH. At higher cofilin-to-actin ratios, a nonpolymerizable cofilin-G-actin complex forms resulting in a decreased rate of polymerization. The data from fluorescence photobleaching recovery experiments at low cofilin-to-actin ratios are consistent with the presence of severed filaments at both pH 8 and 6.6. However, at pH 8 and a cofilin-to-actin ratio of 1:16, about 40-50% of the total actin is present as G-actin after polymerization while at pH 6.6 little or no G-actin is present at the same cofilin-to-actin ratio. The results suggest some cooperativity with respect to cofilin binding to filamentous actin which may be pH dependent.
authors.affiliation: Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, Saint Louis, Missouri 63110, USA.
authors.forename: J
authors.initials: J
authors.lastname: Du
authors.forename: C
authors.initials: C
authors.lastname: Frieden
mesh_terms: D051339:Actin Depolymerizing Factors; D000199:Actins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D015153:Blotting, Western; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008840:Microfilament Proteins / Q000737:chemistry* / Q000378:metabolism*; D010777:Photochemistry; D012441:Saccharomyces cerevisiae; D013050:Spectrometry, Fluorescence
chemical_list: D051339:Actin Depolymerizing Factors; D000199:Actins; D008840:Microfilament Proteins