Abstract
We describe the purification procedure and some of the physiochemical properties of gelsolin, a major Ca2+-dependent regulatory protein of actin gel-sol transformation in rabbit lung macrophages. Gelsolin accounts for the majority of Ca2+ control of actin gelation in macrophage extracts. It is a single polypeptide chain with an average molecular weight of 91,000 a Stokes radius of 44 A, a sedimentation coefficient (s20(0),w) of 4.9 S, an isoelectric point of 6.1, and a frictional ratio of 1.43. Gelsolin binds 2 mol of Ca2+ with high affinity (Ka 1.09 X 10(6) M-1) in the presence of 0.1 M KCl and 2 mM MgCl2.
Highlights
"Calculated assuming a molecular weight of 91,OOO for gelsolin subunit
Actin-binding protein is the major actin-gellingfactor in macrophages, accounting for at least 70%of total gelling activity in SI.Second, the gelation of actin by actin-binding protein in the absence of gelsolin is not inhibited by Ca2+.gelsolin is the only protein in macrophages which inhibits gelation of actin by actin-binding protein in the presence of micromolar Cap+.We did not detect significant activity with the properties of "actinogelin," a calcium-sensitive actin-gelling protein reported to exist in Ehrlich ascites ceUs (Mimura and Asano, 1979)
Free calcium concentration was expressed in p ~Th. e line is fitted by linear regression analysis, and the coefficient of correlation was 0.9914
Summary
"Calculated assuming a molecular weight of 91,OOO for gelsolin subunit. We conclude that the bulk of the Ca2'-sensitive solation activity in macrophage extracts can be accounted for by the effect of gelsolin on actin-actinbinding protein gel formation. Actin-binding protein is the major actin-gellingfactor in macrophages, accounting for at least 70%of total gelling activity in SI.Second, the gelation of actin by actin-binding protein in the absence of gelsolin is not inhibited by Ca2+.gelsolin is the only protein in macrophages which inhibits gelation of actin by actin-binding protein in the presence of micromolar Cap+.We did not detect significant activity with the properties of "actinogelin," a calcium-sensitive actin-gelling protein reported to exist in Ehrlich ascites ceUs (Mimura and Asano, 1979).
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