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BIOCATALYSIS BY NOVEL METAL CLUSTERS AND HYDROGENASE (STRUCTURE REACTIVITY AND IMMOBILIZATION)

Objective

PROTEINS CONTAINING METAL IONS DO CATALYSE MANY IMPORTANT BIOLOGICAL REACTIONS, NAMELY THOSE INVOLVING TRANSFER OF ELECTRONS. IT IS ANTICIPATED THAT MODIFICATIONS OF THE METAL CLUSTERS OF THESE PROTEINS WILL OPEN NEW CATALYTIC POSSIBILITIES THAT CAN BE USED IN MULTIPHASE BIOCATALYSIS AND THE DEVELOPMENT OF NOVEL BIOREACTORS. THE DESIGN OF SUCH CATALYSTS OBTAINED BY A BIOSYNTHETIC ROUTE MAY TURN OUT TO BE ADVANTAGEOUS IN COMPARISON WITH CHEMICAL SYNTHETIC ONES AND CAN THUS SUBSTANTIALLY EXPAND THE FIELD OF BIOINORGANIC CHEMISTRY.
Iron sulphur proteins are involved as main catalysts in bioconversion processes (hydrogen evolution, nitrogen and carbon monoxide fixation, photosynthesis, respiration, etc). The metal active centres of different iron sulphur proteins (simple and complex, eg rubredoxin, ferredoxins and hydrogenase) were characterised and chemically modified, in order to produce new active structures with novel, and/or enhanced catalytic properties. A new concept of assisted inorganic synthesis by a protein template was developed for the synthesis of mixed metal clusters. The reactivity and stability of the newly formed catalysts and hydrogenase (free and immobilised) were tested by measuring hydrogen evolution/production, deuterium(2)/hydrogen(+) exchange (mass spectrometry) and hydrogenation activity. Another important goal was to develop an adequate system to test hydrogenation activity in a multiphase biocatalyst system with immobilised hydrogenase or bacterial cells.

Iron sulfur proteins are involved as main catalysts in bioconversion processes (hydrogen evolution, nitrogen and carbon monoxide fixation, photosynthesis, respiration, etc). The metal active centres of different iron sulfur proteins, simple and complex, (eg, rubredoxin, ferredoxins and hydrogenase) were characterized and chemically modified, in order to produce new active structures with novel, and/or enhanced catalytic properties. A new concept of assisted inorganic synthesis by a protein template was developed for the synthesis of mixed metal clusters. The reactivity and stability of the newly formed catalysts and hydrogenase (free and immobilized) were tested by measuring hydrogen evolution and production, deuterium protium exchange (mass spectroscopy) and hydrogenation activity.

The following results were obtained (from research into the structure, reactivity and immobilization of metalloproteins:
isomorphous substitutions (cobalt and nickel) of the iron centre in rubredoxins:
chemical and spectroscopic characterization;
testing biocatalytic performance and mimicking of bacterial hydrogenase activity (model design);
assisted inorganic synthesis of novel mixed metal clusters of the type M, 3 iron-4 sulphur (M = cobalt, nickel, zinc, cadmium, calcium);
spectroscopic studies involving electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR) and Moessbauer methods;
characterization of the metal sites involved in bacterial hydrogen production and consumption;
differentiation of hydrogenase types by their spectroscopic, catalytic and inhibition parameters;
biocatalysis in organic media using hydrogenase encapsulated in micellar systems;
kinetics of both free and immobilized hydrogenases;
stability of the hydrogen evolving system in reversed micellar systems (multiphase system) using purified hydrogenase and whole cells.
THE 3 MAIN OBJECTIVES OF THE RESEARCH WILL BE :
- TO STUDY DIFFERENT FE-S CENTERS CONTAINING PROTEINS (IN PARTICULAR RUBREDOXIN, FERREDOXIN AND HYDROGENASE) BY RECONSTITUTION EXPERIMENTS. THE FOLLOWING MODIFIED METALLOPROTEINS WILL BE PREPARED, PURIFIED AND CHARACTERISED :
57FE LABELLED RUBREDOXIN AND FERREDOXIN (FD);
CO AND NI SUBSTITUTED RUBREDOXINS;
RECONSTITUTED METALLOPROTEINS FROM MEDIA CONTAINING DIFFERENT METAL IONS PROPORTIONS (NI/FE, CO/FE AND MO/FE) OR BY USING SELENIUM INSTEAD OF SULPHUR.
- TO STUDY MIXED METAL CLUSTERS. THE FOLLOWING METALS WILL BE INTRODUCED IN THE IRON-SULFUR CORE OF DESULFOVIBRIO GIGAS FERREDOXIN :ZN, CU, GA, CD, CO, NI AND MO. THE REDOX POTENTIAL, THE STRUCTURAL FEATURESS AS WELL AS THE CORE STABILITY OF THE NOVEL STRUCTURES WILL BE STUDIED IN ORDER TO BE ABLE TO DESIGN NEW CATALYSTS AND NEW MODEL COMPOUNDS.
- THESE STUDIES WILL BE FURTHER EXTENDED TO THE ALTERATION OF THE ACTIVE CENTRE OF A COMPLEX ENZYME (D.GIGAS HYDROGENASE CONTAINING 3 FE AND 4 FE CENTERS AND 1 NI ATOM). A SELECTIVE MODIFICATION OF SUCH AN ENZYME WILL BE INFORMATIVE FOR MECHANISTIC STUDIES.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

UNIVERSIDADE NOVA DE LISBOA
Address
Centro De Quimica Estrutural Complexo I Av. Rovisco Pais
1000 Lisboa
Portugal

Participants (2)

Association pour la Recherche en Bioénergie Solaire
France
Address
Centre D'études De Cadarache Sere-ders
13108 Saint-paul-lez-durance
Instituto Superior Tecnico
Portugal
Address

Lisboa