Effect of poly(vinyl acetate-acrylamide) microspheres properties and steric hindrance on the immobilization of Candida rugosa lipase.

Poly(vinyl acetate-acrylamide) microspheres were synthesized in the absence or presence of isooctane via suspension polymerization and utilized as carriers to immobilize Candida rugosa lipase. When the hydrophobic/hydrophilic surface characteristics of the microspheres were modified by changing the ratio of vinyl acetate (hydrophobic monomer) to acrylamide (hydrophilic monomer) from 50:50 to 86:24, the immobilization ratio changed from 45% to 92% and the activity of the immobilized lipase increased from 202.5 to 598.0 U/g microsphere. Excessive lipase loading caused intermolecular steric hindrance, which resulted in a decline in lipase activity. The maximum specific activity of the immobilized lipase (4.65 U/mg lipase) was higher than that of free lipase (3.00 U/mg lipase), indicating a high activity recovery during immobilization.

Improving immobilization of lipase onto magnetic microspheres with moderate hydrophobicity/hydrophilicity.

Magnetic microspheres with carboxyl groups were prepared by copolymerization of vinyl acetate (VAC), acrylamide (AM), and acrylic acid (AA) in the presence of oleic acid-coated Fe(3)O(4) nanoparticles. Scanning electron microscope (SEM) photo showed that the average diameter of magnetic microspheres was about 400 nm. Also, FTIR spectra analysis indicated that monomers were successfully enfolded on the microspheres' surface. They were used as support to immobilize lipase via physical adsorption and covalent binding. To investigate the effect of the microsphere surface properties on lipase immobilization, a series of microspheres with different hydrophobic/hydrophilic surface characteristics were prepared by adjusting molar percentages of different monomers. The results showed that microspheres with different hydrophobicities/hydrophilicities had different immobilized ratios and different activity recovery. Compared with microspheres having hydrophilic characteristics, that with hydrophobic characteristics had a much higher lipase binding efficiency. However, this study further demonstrated that moderate hydrophobicity/hydrophilicity of microsphere surface was very important for elevating activity recovery. When AM (hydrophilic monomer) held 14.3% of total amount of monomers, the activity recovery was the highest (reaching 87%, 418 U/g support). Possible reasons for these observations were discussed and a supposed mechanism was speculated.

Kinetic biosynthesis of L-ascorbyl acetate by immobilized Thermomyces lanuginosus lipase (Lipozyme TLIM).

Thermomyces lanuginosus lipase (Lipozyme TLIM)-catalyzed esterification of L-ascorbic acid was studied. It was suggested that Lipozyme TLIM was a suitable biocatalyst for enzymatic esterification of L-ascorbic acid. Three solvents were investigated for the reaction, and acetone was found to be a suitable reaction medium. Furthermore, it was found that water activity could notably affect the conversion. Moreover, pH memory of Lipozyme TLIM lipase for catalyzing L-ascorbic acid esterification in acetone was observed and the effect of pH on the reaction was estimated. In addition, the influences of other parameters such as substrate mole ratio, enzyme loading, and reaction temperature and reusability of lipase on esterification of L-ascorbic acid were also analyzed systematically and quantitatively. Kinetic characterization of Lipozyme TLIM showed that K(m,a) and V(max) were 80.085 mM and 0.747 mM min(-1), respectively. As a result, Lipozyme TLIM-catalyzed esterification of L: -ascorbic acid gave a maximum conversion of 99%.