Effect of pressure on catalytic properties of glutamate racemase from Aquifex pyrophilus, an extremophilic bacteria

The effect of pressure on the catalytic properties of glutamate racemase from Aquifex pyrophilus, an extremophilic bacterium, was investigated. The activation volume for the overall reaction (ΔV^≠) and catalysis (ΔV^≠_cat) was -96.97 ml/mol and 4.97 ml/mol, respectively, while the reaction volume for the substrate binding (ΔV_Km-1) was -101.94 ml/mol. The large negative ΔV^≠ for the overall reaction indicated that the pressurization of glutamate racemase resulted in enhanced catalytic efficiencies. In addition, this value was also due to the large negative ΔV_Km-1 for the substrate binding. The negative value of ΔV_Km-1 implied that the conformational changes in the enzyme molecule occurred during the substrate binding process, thereby increasing the degree of hydration. The small value of ΔV^≠_cat suggested that the pressure did not affect the glutamate racemase catalysis after the substrate binding.