Characterization of horse plasma gelsolin.

Gelsolin can be purified from horse blood plasma by treating the plasma sequentially with an anion-exchange medium in the presence and then the absence of free Ca2+. The purified gelsolin migrates as a 90-kilodalton protein on electrophoresis in polyacrylamide gels in the presence of sodium dodecyl sulfate. It has an absorption coefficient of 1.4 mL/(mg.cm) and is similar in amino acid composition to other plasma gelsolins. Horse plasma gelsolin has an intrinsic sedimentation coefficient of 4.8S and a Stokes' radius of 3.8 nm. Hydrodynamic calculations suggest it to be a rather globular protein of 75,000 relative mass, a value similar to those calculated for human and pig plasma gelsolins from their amino acid sequences. Horse plasma gelsolin is able to nucleate actin polymerization, i.e., to abolish the lag observed between the initiation of polymerization of monomeric actin by the addition of salts and the rapid elongation phase of actin filament growth. This nucleation activity also results in lower final viscosities of F-actin solutions, as the existence of a larger number of filaments in samples that contain gelsolin requires that their average length be shorter.