Fabrication, characterization, and enzymatic activity of encapsulated fungal protease-fatty lipid biocomposite films

Encapsulation of an aspartic protease from the fungus Aspergillus saitoi (F -prot) in thermally evaporated fatty acid films by a simple beaker-based im mersion technique under enzyme-friendly conditions is described. The approa ch is based on diffusion of the enzyme from aqueous solution, driven primar ily by attractive electrostatic interaction between charged groups on the e nzyme surface and ionized lipid molecules in the film. The encapsulated enz yme molecules could be "pumped out" of the biocomposite film into solution by modulating the electrostatic interaction between the enzyme and fatty ac id molecules via solution pH variation. The kinetics of F-prot diffusion in to the acid films was followed using quartz crystal microgravimetry measure ments while the secondary and tertiary structure of the enzyme in the lipid matrix was studied using Fourier transform infrared (FT-IR) and fluorescen ce spectroscopies. FT-IR and fluorescence measurements indicated little per turbation to the native structure of the enzyme. A chemical analysis of the F-prot-fatty acid biocomposite film was also performed using X-ray photoel ectron spectroscopy. The encapsulated F-prot molecules showed catalytic act ivity las estimated by reaction with hemoglobin) comparable to free enzyme molecules in solution, indicating facile access of biological analytes/reac tants in solution to the enzyme molecules. The advantages/disadvantages of this approach vis-a-vis methods currently used for encapsulation of biomole cules are briefly discussed.