An Enzyme Net Coating the Surface of Nanoparticles: A Simple and Efficient Method for the Immobilization of Phospholipase D

Phospholipase D (PLD) was immobilized in a simple and effective way by adsorption and precipitation of the enzyme, followed by chemical cross-linking to form an “enzyme net” covering the surface of nonporous silicon dioxide nanoparticles. For catalyzing transphosphatidylation to produce phosphatidylethanolamine (PE), at pH 6.0 and 35 °C (the optimum operational conditions), the specific activity of immobilized PLD reached 15872 U/g_protein, which was approximately 1.15 times higher than the maximum value of specific activity of free PLD (13813 U/g_protein). A kinetic study demonstrates immobilized PLD had increases in catalytic activity and enzyme–substrate affinity. In addition, the thermostability and pH tolerance were significantly enhanced compared with free PLD. The half-life of immobilized PLD was significantly increased from 30 to 70 days at 4 °C (approximately 2.3 times). This novel method has been proven to be suitable for the production of robust biocatalysts

High-Yield and Sustainable Production of Phosphatidylserine in Purely Aqueous Solutions via Adsorption of Phosphatidylcholine on Triton-X-100-Modified Silica

Triton X-100 was covalently bound to a surface of silica and acted as an anchor molecule to facilitate the adsorption of phosphatidylcholine (PC) in a purely aqueous solution. The silica-adsorbed PC obtained was successfully used for phospholipase D (PLD)-mediated transphosphatidylation in the production of phosphatidylserine (PS). Organic solvents were completely avoided in the whole production process. The PC loading and PS yield reached 98.9 and 99.0%, respectively. Two adsorption models were studied, and the relevant parameters were calculated to help us understand the adsorption and reaction processes deeply. In addition, the silica-adsorbed PC provides a promising way to continuously biosynthesize PS. A packed-bed reactor was employed to demonstrate the process flow of the continuous production of PS. The recyclability and stability of the Triton-X-100-modified silica were excellent, as demonstrated by its use 30 times during continuous operation without any loss of the productivity