Germany — Lipid mono- and bilayer supported on polymer films: Composite polymer- lipid films on solid substrates

Germany — Lipid mono- and bilayer supported on polymer films: Composite polymer- lipid films on solid substrates

Biosensors & Bioelectronics VoL 10 No. I/2 (1995) hydrochloride), which further confirms the assumption that the former subpopulation is the active f...

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Biosensors & Bioelectronics VoL 10 No. I/2 (1995)

hydrochloride), which further confirms the assumption that the former subpopulation is the active form of the immobilized enzyme and the latter subpopulation is the denatured form. Moreover, denaturation at elevated temperature can also c o n v e r t s u b p o p u l a t i o n A into subpopulation D. (6) By paramagnetic relaxation mechanisms, which require close proximity of the paramagnetic species and the spin label, K3Fe (CN)6 can broaden the EPR signal of spin label bound to subpopulation A but not that of subpopulation D, suggesting that subpopulation A is accessible to the substrate. More direct evidence that subpopulation A is the active form of the immobilized enzyme and more accessible to substrate than subpopulation D was obtained by immobilizing papain on modified polysulfone membranes first followed by spin labeling. In this way, only the active subpopulation A was labeled by the spin label. (7) The Km(app) values of the immobilized papain are larger than that of papain in solution, while Vmax(app) is smaller. (8) The enzyme is highly reusable and has very high storage stability after immobilization. (9) Papain immobilized on polysulfone membranes has much higher thermal stability and stability toward denaturants (urea or guanidine hydrochloride) than that of free papain in solution. In this study the p o l y m e r i c m e m b r a n e provided three functions: sites for covalent coupling of enzymes; enhanced enzyme stability; and substrate partitioning. The paper reports the first development of an effective method to acquire EPR spectra of fully-hydrated, spin-labeled enzymes immobilized on polymeric membranes. All these findings indicate that the EPR spin-labeling technique shows great promise as a powerful method for studying membrane-immobilized enzyme systems.

Contact: Department of Chemistry, University Kentucky, Lexington, KY 40506-0055, USA.

Germany - Lipid mono- and bilayer supported on polymer films: Composite polymer- lipid films on solid substrates In BIOPHYS. J. (67/1 (217-226) 1994)) M. Kuhner, R. Tampe and E. Sackmann of Munich's Max-Planck-Institut fur Biochemie report Lipid mono- and bilayer supported on polymer films: C o m p o s i t e p o l y m e r - l i p i d films on solid substrates. The authors report the deposition of lipid monolayers and bilayers on polyacrylamide films deposited by radical chain reaction onto solid substrates in aqueous solutions. Polymer films of various degrees of monomer density and cross-linking are prepared. Lateral diffusion and fluorescent probe permeation measurements yield insight into the continuity of the lipid layers and show that monolayers exposed to air are much less sensitive towards polymer heterogeneities than bilayers below water, which is explained in terms of the wetting laws. The diffusion studies of lipid and lipopeptide probes yield absolute values of the frictional coefficients between the lipid layer and the polymer films and allow one to estimate the surface viscosity of the polymer film. The potential applications of supported membranes on soft thin polymer films for the preparation of biofunctionalized surfaces or biocompatible receptive surfaces for biosensors are discussed.

Contact: Max-Planck-lnstitutfur Biochemie, Am Klopferspitz 18a, D-82152 Martinsried, Munchen, Germany Japan - Response of polyacrylamide-benzo-15-crown-5 coated platinum electrode to calcium ion and some other cations in propylene carbonate and its thermodynamic application In ANAL. CHIM. ACTA (292/3 (305-310) 1994)) T. Nakamura, C. Hayashi and K. Izutsu of Shinshu U n i v e r s i t y report on " R e s p o n s e of polyacrylamide-benzo- 15-crown-5 coated platinum electrode to calcium ion and some other cations in p r o p y l e n e c a r b o n a t e and its thermodynamic application".

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