UreE, a urease accessory protein, is proposed to be a metallochaperone assisting the nickel incorporation into the urease active site. We investigated the e¡ects of salt and nickel on the conformational stability of the UreE from Bacillus pasteurii (BpUreE), by circular dichroism (CD) and nuclear magnetic resonance spectroscopy accompanying a thermodynamic inspection. Far-UV CD spectra of BpUreE showed that both salt and nickel stabilized the ordered structure of the protein. The thermal denaturing of BpUreE showed a bimodal feature with an aggregation process before thermal unfolding. This thermally induced aggregation could be suppressed by the addition of salt up to 50 mM, and the further addition of salt increased the thermal resistance of the protein. The nickel addition also elevated the thermal resistance of BpUreE, although it could not prevent the aggregating process. Additionally, the stoichiometry of a speci¢c nickel binding to BpUreE was revealed as one nickel per dimer. Altogether, the present results establish a rather detailed characterization of the thermostability and nickel-binding property of BpUreE. ß

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Orally administrated drugs permeate the biological membrane by various transport mechanisms. The oral absorption potential is closely related to the physicochemical properties of the drug and interaction with the physiological factors surrounding the site of absorption. Assessment of the drug membrane permeability is an integral part of the early stage drug developmental process. Appropriate selection of the permeability screening method at the right stage of drug development process is important in achieving successful developmental outcomes. This review aims at introducing currently available in vitro and in vivo screening methods for the membrane permeability assessment.