Abstract
We purified profilin from rabbit alveolar macrophages and documented its structural and functional similarity to profilins isolated from other cells. The KD for formation of the macrophage profilin-actin complex was 3.0 +/- 0.8 microM (mean +/- S.D.). The affinity of this protein for actin did not change significantly in the presence of various concentrations of KCl and MgCl2, profilin-actin complex concentration being strictly dependent on the critical actin monomer concentration and free profilin concentration. We also examined profilin's interactions with actin in the presence of acumentin, a macrophage protein which inhibits actin monomer exchange at the "pointed" ends of actin filaments. Low concentrations of this protein caused substantial decreases in estimated profilin-actin complex concentration. The macrophage gelsolincalcium ion complex which blocks exchange at the "barbed" end of actin filaments, when added to profilin and actin solutions in substoichiometric concentrations, caused large increases in estimated profilin-actin complex concentration. The changes in calculated profilin-actin complex concentration induced by these two actin-modulating proteins were too large to be explained solely by their effects on critical actin monomer concentration.
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