Significant Decrease in the Solubility of Glucose Isomerase Crystals under High Pressure

Solubility of glucose isomerase (from Streptomyces rubiginosus ) crystals was measured in situ at 0.1 and 100 MPa. An equilibrium temperature of the crystal with the solution of a given concentration was measured using a two-beam interferometer. The solubility of the crystal decreased to about one-ninth with increasing pressure from 0.1 to 100 MPa at 30 °C. This means that the supersaturation, σ (= ln C / C e, C = protein concentration, C e = solubility), increases significantly with increasing pressure at the same temperature. This strongly suggests that the substantial acceleration of the crystallization of glucose isomerase with increasing pressure reported by Visuri et al. is due to the significant decrease in the solubility. The enthalpy and entropy of the dissolution were estimated from the van't Hoff plots. The volume change accompanying the dissolution took a large positive value as Δ V = 54 ± 31 cm 3 mol -1 at 30 °C.