Theoretical Investigation into the Change in the Number of Water Molecules in Solvent Inaccessible Region of an Enzyme and Enzyme-substrate Complex
Ikechukwu Iloh Udema *
Research Division, Ude International Concepts Limited, (RC 862217), B. B. Agbor, Delta State, Nigeria and Department of Biochemistry and Chemistry, Owa Alizomor Secondary School, Owa Alizomor, Ika North East, Delta State, Nigeria.
Abraham Olalere Onigbinde
Department of Biochemistry, Faculty of Life Sciences, Ambrose Alli University, Ekpoma, Nigeria.
*Author to whom correspondence should be addressed.
Abstract
Background: There may be dry enzymes, but water remains indispensable for the catalytic action of enzymes. There is not as much interest in how the presence of a drug such as aspirin and a psychoactive compound such as ethanol may affect the water-mediated role of the enzyme.
Objectives: The objectives of this research are: 1) To assess the changes in the number of water molecules interacting with the enzyme-substrate complex and the solvent inaccessible region of a protein, 2) to determine the free energy difference due to preferential solvation and hydration, and 3) to re-examine theoretical issues in literature and relate them to the interpretation of the results.
Methods: A major theoretical research and minor experimentation using Bernfeld method.
Results and Discussion: The presence of ethanol/aspirin alone yielded only dehydration of the osmolyte inaccessible region and the enzyme substrate complex (ES). There was positive free energy difference (DDG) if the equilibrium constant for hydration change (Keq(1))> the equilibrium constant for folding-unfolding transition (Keq(3)); it is negative where Keq(3)> Keq(1). Analysis of various models made them valuable for the interpretation of result for feature application.
Conclusion: The change in the number of water molecules in an osmolyte inaccessible region of the enzyme and those interacting with the ES may be either positive or negative due respectively to sucrose and ethanol/aspirin. The spontaneity of two processes, hydration and folding-unfolding transition, the free energy difference, differs. The model for water stripping, preferential interaction concept, and the KBI for osmolation and hydration can guide the interpretation of the effects of any cosolute.
Keywords: Porcine pancreatic alpha amylase, change in gibbs free energy, change in the number of water molecules, enzyme-substrate complex, osmolyte-inaccessible region of enzyme, cosolutes, Kirkwood-Buff Integrals(KBI).