Quasielastic light scattering, electrophoresis, and fluorescence studies of lysozyme‐poly(2‐acrylamido‐methylpropylsulfate) complexes

Complexation between lysozyme and sodium poly(2‐acrylamido‐2‐methylpropanesulfonate) (PAMPS) was studied by quasielastic light scattering, electrophoretic light scattering, fluorescence, and turbidimetry in electrolyte solution. These techniques show that complexation occurs at pH 9.6 in an ionic strength buffer of 0.25M NaCl + 25 mM Na2B4O7. At constant lysozyme concentration (Cpro). The structure of the complex depends on the polymer concentration. At low polymer concentration (relative to Cpro), an intrapolymer complex is formed. This intrapolymer complex aggregates to an interpolymer species upon increase in polymer concentration. Complex formation was also studied by fluorescence using pyrene‐labeled PAMPS (Py‐PAMPS). Energy transfer from singlet‐excited tryptophan residues in lysozyme to the pyrene label occurs when the complex is formed. Fluorescence and turbidity data indicate that lysozyme interacts with Py‐PAMPS preferentially at pyrene sites, which leads to static quenching of tryptophan fluorescence via energy transfer to the pyrene label.