Soluble enzyme system for vitamin K-dependent carboxylation.

Area of Science:

• Biochemistry
• Enzymology
• Molecular Biology

Background:

• The vitamin K-dependent carboxylating system is crucial for post-translational modification of proteins.
• Solubilization of membrane-bound enzyme systems is essential for detailed biochemical characterization.

Purpose of the Study:

• To solubilize and characterize the vitamin K-dependent carboxylating system from rat liver microsomes.
• To investigate the cofactor requirements and properties of the soluble carboxylating enzyme.

Main Methods:

• Rat liver microsomes from vitamin K-deficient rats were treated with detergents (Lubrol PX or Triton X-100) to achieve solubilization.
• The carboxylating activity of the soluble preparation was assayed in vitro, with varying additions of vitamin K1, NADH, and dithiothreitol.
• Enzyme inhibition studies using p-hydroxymercuribenzoate were conducted.

Main Results:

• A soluble vitamin K-dependent carboxylating system was successfully obtained from rat liver microsomes.
• The solubilized system demonstrated vitamin K1-dependent carboxylating activity.
• Maximum activity required NADH and dithiothreitol, and the system was inhibited by p-hydroxymercuribenzoate, suggesting the involvement of a sulfhydryl (SH) enzyme.

Conclusions:

• The vitamin K-dependent carboxylating system can be effectively solubilized using non-ionic detergents.
• The solubilized enzyme requires vitamin K1, NADH, and dithiothreitol for optimal activity.
• Evidence suggests that a sulfhydryl (SH) enzyme is integral to the vitamin K-dependent carboxylation process.