Effects of head group of cationic surfactants on the hydrolysis ofp-nitrophenyl acetate catalyzed by α-chymotrypsin

Controllable enzymatic superactivity of α-chymotrypsin activated by the electrostatic interaction with cationic gemini surfactants

Surfactant plays a critical role in enzymatic multi-functionalization processes. However, a deep understanding of surfactant-enzyme interactions has been lacking up until now due to the extreme complexity of the mixed system. This work reported the effect of cationic gemini surfactants, alkanediyl-α,ω-bis(dimethyldodecylammonium bromide) (C12C S C12Br2, S = 2, 6, and 10) on the enzymatic activity and conformation of α-chymotrypsin (α-CT) in phosphate buffer solution (PBS, pH 7.3). The enzymatic activity was assessed by the rate of 2-naphthyl acetate (2-NA) hydrolysis measured by UV-vis absorption. The superactivity of α-CT in the presence of C12C S C12Br2 appears in the concentration region below the critical micelle concentration (cmc) of the surfactant, and its maximum superactivity is correlated to the spacer length of C12C S C12Br2. Subtle regulation of the charge density of headgroups of the cationic surfactant can be achieved through partial charge neutralization of cationic headgroups by introducing inorganic counterions or oppositely charged surfactant, demonstrating that the electrostatic interaction plays the crucial role for emergence of the superactivity. The interaction between C12C S C12Br2 (S = 2,6, and 10) and α-CT was characterized by isothermal titration calorimetry (ITC), and the obtained endothermic enthalpy change indicates that the interaction induces the change in conformation and enzymatic superactivity. The methodologies of fluorescence spectroscopy, circular dichroism (CD), and differential scanning calorimetry (DSC) show that the gemini surfactants with different spacer lengths induct and regulate the secondary, tertiary and even fourth structures of the protein. The present work is significant to get deeper insight into the mechanism of the activation and denaturation of enzymes.

Enhanced Catalytic Activity of α-Chymotrypsin in Cationic Surfactant Solutions: The Component Specificity Revisited

Enhanced catalytic activity (super activity) of enzymes in the presence of surfactants is of key importance in "micellar enzymology"; such super activity is not very trivial, it is highly system specific, and the mechanism behind the activity enhancement is not always well apprehended. We report the catalytic activity of α-chymotrypsin (CHT) on ala-ala-phe-7-amido-4-methylcoumarin (AMC) in the presence of cationic surfactants of different hydrophobic chain lengths: dodecyltrimethylammonium bromide (DTAB), cetyltrimethylammonium bromide (CTAB) and octadecyltrimethylammonium bromide (OTAB). It is observed that in comparison to buffer the catalytic activity of CHT is enhanced 5-fold in premicellar DTAB solutions, while negligible changes are observed in CTAB and OTAB. Activity decreases considerably in the post micellar concentration, specifically for the latter two surfactants. A similar trend is also obtained in another substrate 2-napthyal acetate hydrolysis. Such surfactant specific superactivity is intriguing. The protein's secondary and tertiary structures in the presence of these surfactants are determined using circular dichroism (CD) spectroscopy and it is found that both CTAB and OTAB perturb the protein structure significantly, especially in the post micellar concentrations. DTAB, on the other hand, does not produce noticeable changes in the protein structure. The various pairwise interactions present in the system have been underlined using both steady-state and time-resolved fluorescence spectroscopy. Assuming a three-step kinetics model, we determine the free energy changes of the reaction, and the observations have been discussed in the light of the various interactions among the components.

α-Chymotrypsin superactivity in quaternary ammonium salt solution: kinetic and computational studies

Ammonium salts determine an increase of the hydrophobicity of the α-chymotrypsin catalytic site and therefore an improvement of its activity.

Effects of Surfactants on the Rate of Chemical Reactions

Surfactants are self-assembled compounds that depend on their structure and electric charge can interact as monomer or micelle with other compounds (substrates). These interactions which may catalyze or inhibit the reaction rates are studied with pseudophase, cooperativity, and stoichiometric (classical) models. In this review, we discuss applying these models to study surfactant-substrate interactions and their effects on Diels-Alder, redox, photochemical, decomposition, enzymatic, isomerization, ligand exchange, radical, and nucleophilic reactions.