A dialysis technique for determining aggregate concentrations in crystallizing protein solutions

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Abstract
The authors have adapted a dialysis technique which provides aggregate concentrations of protein molecules in solutions which lead to crystal growth. In dialysis, the flux across a semipermeable membrane is directly proportional to the concentration of the diffusible solute inside the bag provided that the solute concentration in the bulk solution is infinitely dilute. Using membranes of varying porosity, the concentrations of different size solutes can be measured by measuring the flux rate across the membrane. They have used this technique to independently measure the concentrations of monomers, dimers, trimers and higher aggregates of lysozyme in both 1% NaCl and 3% NaCl (0.1 M NaAc, pH4) using 25 K and 50 K molecular weight cut-off membranes. They compare these concentration profiles with (110) face growth rate data under the same conditions.