Analytical titration curves of glycosyl hydrolase Cel45 by combined isoelectric focusing-electrophoresis

The electrical charge of endocellulase Cel45-core has been determined by co mbined isoelectric focusing-electrophoresis in the range of pH 3-9. In orde r to transform electrophoretic mobility to absolute electrical charge value , several corrections were applied: the frictional coefficient theoreticall y calculated from the molecular dimensions depends on porous gel structure and on the ionic strength of the solution. By comparing the curve calculate d according to the Linderstrom-Lang equation, the number of charged electri cal groups exposed to the solvent and their apparent ionization constants, pK(i)(o), can be determined. Furthermore, the macromolecule structure can b e assumed not to change in this pH range. This finding is necessary to unde rstand the structure and the electrical properties of the entire Cel45 mole cule.