Stimulation of the vitamin K-dependent carboxylase from bovine liver

Vitamin K-dependent carboxylase from bovine liver is stimulated not only by reducing agents and bivalent metal ions (especially Mn2+), but also by several organic solvents (dimethyl sulphoxide, ketones and acetonitrile). The organic solvents stimulated both the carboxylation of glutamic acid residues and the formation of vitamin K epoxide. This stimulation by organic solvents was independent of the physical state of the phospholipid; it was highest at low temperatures and could only be demonstrated with vitamin K1 and not with 3-DTT-MK-O (the thioether adduct of menadione and dithiothreitol) or t-butyl hydroperoxide, which normally can substitute for vitamin K. We suggest that organic solvents exert their effect by changing the mobility of the isoprenoid side chain of vitamin K1 within the carboxylase complex.