Altered conformation of Gc (vitamin D-binding protein) upon complexing with cellular actin.

Complexing of serum Gc (Vitamin D-binding protein) with cellular actin can occur in the extracellular space as a result of cell turnover, and particularly cell necrosis. The clearance of such complexes is significantly more rapid than that of Gc alone, and several tissues are involved in their uptake, but the mechanisms involved are unknown. We present evidence here that interaction with actin results in alteration of certain physicochemical properties of Gc. Fluorescence of the hydrophobic probe 2-p-toluidinylnaphthylene-6-sulfonate was abolished by complex formation with actin. In addition, isoelectric focusing of complexes between Gc, and actin from different tissues, revealed that complexes were generally more acidic than either protein individually. These findings indicate that complexing of Gc with actin results in altered conformation.