Characterization of redox proteins from extreme thermophilic archaebacteria: studies on alcohol dehydrogenase and thioredoxins

Enhancing the functional properties of thermophilic enzymes by chemical modification and immobilization

The immobilization of proteins (mostly typically enzymes) onto solid supports is mature technology and has been used successfully to enhance biocatalytic processes in a wide range of industrial applications. However, continued developments in immobilization technology have led to more sophisticated and specialized applications of the process. A combination of targeted chemistries, for both the support and the protein, sometimes in combination with additional chemical and/or genetic engineering, has led to the development of methods for the modification of protein functional properties, for enhancing protein stability and for the recovery of specific proteins from complex mixtures. In particular, the development of effective methods for immobilizing large multi-subunit proteins with multiple covalent linkages (multi-point immobilization) has been effective in stabilizing proteins where subunit dissociation is the initial step in enzyme inactivation. In some instances, multiple benefits are achievable in a single process. Here we comprehensively review the literature pertaining to immobilization and chemical modification of different enzyme classes from thermophiles, with emphasis on the chemistries involved and their implications for modification of the enzyme functional properties. We also highlight the potential for synergies in the combined use of immobilization and other chemical modifications.

Pyruvate kinase: current status of regulatory and functional properties

Pyruvate kinase (PK) is a key enzyme for the glycolytic pathway and carbon metabolism in general. On the basis of the relevance and enormous diverse properties of this enzyme, this paper describes the results of a current and extensive review that determines the sites of conservation and/or difference in PK sequences, and the differences in the functional and regulatory properties of the enzymes. An alignment and analysis of 50 PK sequences from different sources and a phylogenetic tree are presented. This analysis was performed with reference to crystallographically characterized PK principally from E. coli, cat and rabbit muscle. A number of attributes of the enzyme that make it of particular interest in biomedicine and industry are also discussed.

Pyruvate kinase from the thermophilic eubacterium Bacillus acidocaldarius as probe to monitor the sodium concentrations in the blood

We describe the isolation and characterization of a pyruvate kinase from the thermophilic eubacterium Bacillus acidocaldarius. This protein appears to be a tetramer composed of four 55-kDa subunits. The intrinsic tryptophan fluorescence of this protein is quenched by approximately 20% upon binding sodium, which occurs with a dissociation constant near 15 mM. Importantly, the intrinsic fluorescence of this pyruvate kinase does not appear to be affected by potassium, magnesium, and calcium at the concentrations found in whole blood. It appears that this pyruvate kinase can provide the basis for a selective protein sensor for sodium with minimal interference from other cations.

A hyperactive NAD(P)H:Rubredoxin oxidoreductase from the hyperthermophilic archaeon Pyrococcus furiosus

NAD(P)H:rubredoxin oxidoreductase (NROR) has been purified from the hyperthermophilic archaeon Pyrococcus furiosus. The enzyme is exceedingly active in catalyzing the NADPH-dependent reduction of rubredoxin, a small (5.3-kDa) iron-containing redox protein that had previously been purified from this organism. The apparent Vmax at 80 degrees C is 20,000 micromol/min/mg, which corresponds to a kcat/Km value of 300,000 mM(-1) s(-1). The apparent Km values measured at 80 degrees C and pH 8.0 for rubredoxin, NADPH, and NADH were 50, 5, and 34 microM, respectively. The enzyme did not reduce P. furiosus ferredoxin. NROR is a monomer with a molecular mass of 45 kDa and contains one flavin adenine dinucleotide molecule per mole but lacks metals and inorganic sulfide. The possible physiological role of this hyperactive enzyme is discussed.