Influence of Ascorbic Acid on the Structure and Function of Alpha-2-macroglobulin: Investigations using Spectroscopic and Thermodynamic Techniques

Background: Ascorbic acid is a classic dietary antioxidant which plays an important role in the body of human beings. It is commonly found in various foods as well as taken as dietary supplement. Objective: The plasma ascorbic acid concentration may range from low, as in chronic or acute oxidative stress to high if delivered intravenously during cancer treatment. Sheep alpha-2-macroglobulin (alpha M-2), a human alpha M-2 homologue is a large tetrameric glycoprotein of 630 kDa with antiproteinase activity, found in sheep's blood. Methods: In the present study, the interaction of ascorbic acid with alpha-2-macroglobulin was explored in the presence of visible light by utilizing various spectroscopic techniques and isothermal titration calorimetry (ITC). Results: UV-vis and fluorescence spectroscopy suggests the formation of a complex between ascorbic acid and alpha M-2 apparent by increased absorbance and decreased fluorescence. Secondary structural changes in the alpha M-2 were investigated by CD and FT-IR spectroscopy. Our findings suggest the induction of subtle conformational changes in alpha M-2 induced by ascorbic acid. Thermodynamics signatures of ascorbic acid and alpha M-2 interaction indicate that the binding is an enthalpy-driven process. Conclusion: It is possible that ascorbic acid binds and compromises antiproteinase activity of alpha M-2 by inducing changes in the secondary structure of the protein.