A viscometric study of the effect of PH upon actin polymerization

Actin was isolated and purified from chicken muscle using gel filtration chromatography, spectrophotometry, and gel electrophoresis. The actin was polymerized (G-actin into F-actin) in vitro at pH 8.0 by the addition of MgCl to 2.0 mM and addition of KCl to 0.1 M (in buffer containing 0.2 mM Na2ATP) at room temperature. Viscometry and flow birefringence were carried out at room temperature on 1.0 mg/ml to 0.2 mg/ml samples of F-actin over a gradient of pH 8.0-5.0. Flow birefringence and specific viscosity results indicate the amount of polymerized actin (F-actin) in each sample decreased similarly as a function of declining pH, regardless of initial actin concentration. Intrinsic viscosity data indicate the actin actually was depolymerized, and not denatured, rather dramatically below a threshold of pH 7.0. (See more in text.)