Rapid solubility measurement of protein crystals as a function of precipitant concentration with micro-dialysis cell and two-beam interferometer.

A novel dialysis-based technique was developed for the rapid and sample-saving determination of the precipitant dependence of protein solubility. A unique thin dialysis cell was developed which permits both the direct optical measurement of protein concentration and the observation of concentration gradients around a crystal via two-beam interferometry. Interferograms around a lysozyme crystal under the desired concentrations of precipitant (NaCl) and lysozyme were observed to determine whether the crystal is growing or dissolving. This technique enables the precipitant-dependent solubility curve of lysozyme crystal to be obtained in two days using a small sample (total amount: 7 mg lysozyme).