Enhanced catalytic activity and thermal stability of lipase bound to oxide nanosheets

The present study reports the effects of binding of lipase, which is an inexpensive digestive enzyme (candida antarctica lipase) that catalyzes the hydrolysis reaction and is frequently utilized for artificial synthesis of a variety of organic molecules, to titanate nanosheets (TNSs) on their biocatalytic activities and stabilities under several lipase concentrations. TNSs were prepared through a hydrolysis reaction of titanium tetraisopropoxide (TTIP) with tetrabutylammonium hydroxide (TBAOH), resulting in formation of a colorless and transparent colloidal solution including TNSs with nanometric dimensions (hydrodynamic diameter: ca. 5.6 nm). TNSs were bound to lipase molecules through electrostatic interaction in an aqueous phase at an appropriate pH, forming inorganic-bio nanohybrids (lipase-TNSs). The enzymatic reaction rate for hydrolysis of p-nitrophenyl acetate (pNPA) catalyzed by the lipase-TNSs, especially in diluted lipase concentrations, was significantly improved more than 8 times as compared with free lipase. On the other hand, it was confirmed that heat tolerance of lipase was also improved by binding to TNSs. These results suggest that the novel lipase-TNSs proposed here have combined enhancements of the catalytic activity and the anti-denaturation stability of lipase.

Synergistic Functions of Enzymes Bound to Semiconducting Layers

Synthesis and cooperative functions of hybrid materials composed of enzyme and semiconducting layers are described in this chapter. The hybrids were produced via a simple physical interaction between the components, that is, electrostatic interaction in an aqueous solution. To form interstratifying enzymes in the galleries, solution pH, which is a key parameter to decide surface potential, should be adjusted appropriately. In other words, enzymes should have an opposite charge when compared to that of the layers at an identical pH. Even though the intercalation slightly reduced enzymatic activity as compared to those of the free enzymes, stability under cruel conditions was drastically improved due to screening effect of semiconducting layers from extrinsic stimuli. In addition, photochemical control of redox enzymes sandwiched between semiconducting layers was accomplished. Light irradiation of the hybrids induced band gap excitation of the layers, and holes produced in the valence band activated the enzymes. It was revealed that the semiconducting layers with magnetic elements might be useful to magnetic application (separation) of enzymes as similar to conventional magnetic beads.

Enzyme-mimetic activity of Ce-intercalated titanate nanosheets

Colloidal solutions of Ce-doped titanate nanosheets (Ce-TNS) with tiny dimensions (<10 nm) were fabricated through a hydrolysis reaction of titanium tetraisopropoxide and Ce(NO3)3, and their annihilation activity for reactive oxygen species (ROS) was investigated. The obtained Ce-TNS had an akin crystal structure to layered tetratitanate (Ti4O9(2-)) and Ce ions occupied interlayer space between the host layers with a negative charge. The Ce-TNS possessed a superoxide dismutase (SOD) mimetic activity for disproportionation of superoxide anion radicals (O2(-)) as target ROS. It was explained that the annihilation of O2(-) caused a valence fluctuation of Ce ions existing in the interlayer. Moreover, the activity of Ce-TNS exceeded that of CeO2 nanoparticles recently attracting much attention as an inorganic SOD mimic. The superior performance was explained mainly by a high dispersion stability of the Ce-TNS bringing about a huge reaction area. Moreover, the Ce-TNS protected DNA molecules from ultraviolet light induced oxidative damage, demonstrating effectiveness as one of the new inorganic protecting agents for biomolecules and tissues.

Enhanced catalytic activity of enzymes interacting with nanometric titanate nanosheets

Enzymatic activity of horseradish peroxidase (HRP) at diluted conditions is highly increased under the presence of nanometric titanate nanosheets (TNS).