Superior Activities of Enzymes Physically Immobilized on Structurally Regular Poly(methyl methacrylate) Surfaces

Ultrathin poly(methyl methacrylate) (PMMA) stereocomplex films with macromolecularly double-stranded regular nanostructures were prepared by layer-by-layer (LbL) assembly of isotactic ( it ) and syndiotactic ( st ) PMMAs on solid substrates, and these films were used for enzyme immobilization supports. Hydrolysis of p -nitrophenyl-β- d -galactopyranoside (PNPG) by the immobilized β-galactosidase (β-Gal) on the complex film was 2- and 4-fold faster than those by the enzyme immobilized on single-component it -PMMA and atactic ( at ) PMMA films, respectively. Quartz crystal microbalance (QCM) analysis revealed that greater amounts of β-Gal were immobilized on the complex film through physical adsorption than those on the single-component films. Michaelis constants ( K m ) of the enzyme were independent of film components; however, catalytic efficiencies ( k cat / K m ) were increased by regulation of PMMA conformation at film surfaces. Attenuated total reflection infrared (ATR-IR) analysis revealed that structural denaturation of the enzyme after immobilization processes was well-suppressed on the complex film, although the enzyme on the bare gold or single-component PMMA films were denatured. We propose here that a slight difference of polymer surface structures strongly affects activities of immobilized enzymes, even though polymers have the same chemical component.