The assay of the hydration shell dynamics on the turnover of the active   site of CF1-ATPase
  Previous kinetic models had assumed that the reaction medium was reacting at random and without a turnover associated to thermodynamics exchanges, with a rigid active site on the enzyme. The experimental studies show that coupling factor 1 (CF1) from spinach chloroplasts has latent ATPase activity, which become expressed after heat-treatment and incubation with calcium. The sigmoidal kinetics observed on the competitive effect of glycerol on water saturating a protein, suggests that the role of the hydration shell in the catalytic mechanism of the CF1-ATPase, modify the number of water molecules associated with the conformational turnover required for active site activity. It is assume that the water associated to the hydrophilic state of the enzyme produces a fit-in of the substrate to form (ES), follow by the catalytic action with product formation (EP). This one induces the dissociation of water and increases the hydrophobic attractions between R-groups. The latter, becomes the form of the enzyme interacting with water to form the dissociated free enzyme (E) and free product (P). Glycerol dependent suppression of the water dynamics on two interacting sites configuration shows a change in the H-bond-configuration. The thermodynamics modeling requires an energy expenditure of about 4kcal/mol per each H-bond in turnover. Glycerol determined a turnover of 14 molecules of water released from the active sites to reach the inactive form of the enzyme. The entropy generated by turnover of the fit-in and -out substrate and product from the protein could be dissipated-out of the enzyme-water system itself. Coupling with the surrounding water clusters allows to recreate H-bonds. This should involve a decrease in the number of H-bonds present in the clusters. These changes in the mass action capability of the water clusters could eventually become dissipated through a cooling effect. 
Alfred Bennun
q-bio.BM