Overexpression and purification of Rhizobium etli glutaminase a by recombinant and conventional procedures -: A comparative study of enzymatic properties

Rhizobium etli glutaminase A was purified to homogeneity by conventional procedures that included ammonium sulfate differential precipitation, ion-exchange chromatography, hydrophobic interaction chromatography, gel filtration, and dye-ligand chromatography. Alternatively, the structural glsA gene that codifies for glutaminase A was amplified by PCR and cloned in the expression vector pTrcHis. The recombinant protein was purified to homogeneity by affinity chromatography. This protein showed the same kinetic properties as native glutaminase A (K-m for glutamine of 1.5 mM and V-max of 80 mu mol ammonium min-l mg protein(-1)). Physicochemical and biochemical properties of native and recombinant glutaminase were identical. The molecular mass of recombinant glutaminase A (M-r 106.8 kDa) and the molecular mass of the subunits (M-r 26.9 kDa) were estimated by mass spectrometry. These results suggest that R. etli glutaminase A is composed of four identical subunits. The high-level production of recombinant glutaminase A elevates the possibilities for determination of its three-dimensional structure through X-ray crystallography. (C) 2001 Academic Press.