Interactions of pig plasma gelsolin with G‐actin

Abstract

Pig plasma gelsolin forms a ternary complex with monomeric actin in 0.1 mM CaCl2 and a binary complex in EGTA (< 0.01 .mu.M calcium), as shown by gel filtration and fluorescence changes when actin which had been treated with N-ethylmaleimide and 7-chloro-4-nitrobenzeno-2-oxa-1,3-diazole (NBD-actin) or with N-(1-pyrenyl)iodoacetamide (PI-actin) binds to gelsolin. The fluorescence enhancement per actin molecule bound is similar in the binary and ternary complexes, but the affinity of gelsolin for labelled actin is very much greater in the presence of calcium. Furthermore, the formation of ternarty complex exhibits strong positive cooperativity.