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 th e thermophilic eubacterium Bacillus acidocaldarius. This protein appears to be a tetramer composed of four 55-kDa subunits. The intrinsic tryptophan f luorescence of this protein is quenched by approximately 20% upon binding s odium, which occurs with a dissociation constant near 15 mM. Importantly, t he intrinsic fluorescence of this pyruvate kinase does not appear to be aff ected by potassium, magnesium, and calcium at the concentrations found in w hole blood. It appears that this pyruvate kinase can provide the basis for a selective protein sensor for sodium with minimal interference from other cations. (C) 2000 Elsevier Science B.V. All rights reserved.