Quantitative characterization of temperature-independent polymer–polymer interaction and temperature-dependent protein–protein and protein–polymer interactions in concentrated polymer solutions

Quantitative characterization of non-specific interaction of two globular proteins with Dextran T70 in a binary mixture

In a bid to quantify the contribution of molecular structure to non-specific interactions leading to functionally important structural changes in cellular processes, the self-interaction of dextran-T70 (DT70) and its interaction with each of bovine serum albumin (BSA) and ovomucoid trypsin inhibitor (OVO) were studied at pH 7.4 between 5 and 37 °C. The dependences of the apparent molecular weight of each of BSA, OVO and DT70 on the concentration of DT70 were independent of temperature. The activity coefficient of the interaction of each species on DT70 concentration was also independent of temperature. The change in activity coefficient was however dependent on the molecular structure and size of the interacting species. The energy of insertion of each macromolecule in DT70 increased in the order DT70 > BSA > OVO. These findings show that although the enthalpic contribution is negligible, the extent of the entropic contribution to the macromolecular activity coefficient of interaction is chiefly the consequence of the exclusion volume of the interacting macromolecules.

Catalytic studies of glutathione transferase from Clarias gariepinus (Burchell) in dilute and crowded solutions

Kinetic properties of purified Clarias gariepinus glutathione transferase (CgGST) was studied in the presence of Ficoll 70, Polyethylene glycol (PEG) 6000, bovine serum albumin (BSA) and in dilute solution. This was done to mimic the cytosol thereby unraveling the actual mechanism of detoxication involving glutathione transferase (GST) in the crowded intracellular milieu. CgGST from the liver of Clarias gariepinus was purified to homogeneity by affinity chromatography on glutathione (GSH) - agarose. Initial-velocity study was performed by varying the concentrations of GSH at various fixed concentrations of 1-chloro-2,4-dinitrobenzene (CDNB) and vice-versa. Data obtained were fitted to the three equations representing random-ordered, compulsory-ordered and ping-pong mechanisms to obtain kinetic parameters. Product inhibition studies using sodium chloride (NaCl) was done by varying the concentrations of NaCl and CDNB at a fixed concentration of GSH and vice-versa. Data obtained were fitted to three equations representing competitive, non-competitive and uncompetitive inhibitions to obtain the inhibition constants (K_i^GSH and K_i^CDNB). Optimal temperature of CgGST activity was 20 °C both in dilute and crowded solutions. Maximum velocity (V_max) in dilute solution was decreased, while K_m^GSH and K_m^CDNB were increased in the presence of the crowding agents. Turnover number (k_cat), catalytic efficiency - k_cat/K_m^GSH_,k_cat/K_m^CDNB and inhibition constants - (K_i^GSH and K_i^CDNB) were reduced in crowded solutions. Mechanism of catalysis was steady - state random sequential in both dilute and crowded solutions. The study concluded that although the catalytic efficiency of the enzyme was reduced in crowded solution, mechanism of catalysis remains the same in both crowded and dilute solutions.