Editing Protein quaternary structure (section)

===Indirect size measurement of intact complexes===

* Sedimentation-velocity [[analytical ultracentrifugation]] (measures the translational [[diffusion constant]])
* [[Dynamic light scattering]] (measures the translational [[diffusion constant]])
* Pulsed-gradient [[protein nuclear magnetic resonance]] (measures the translational [[diffusion constant]])
* [[Fluorescence polarization]] (measures the rotational [[diffusion constant]])
* [[Dielectric relaxation]] (measures the rotational [[diffusion constant]])
* [[Dual polarisation interferometry]] (measures the size and the density of the complex)

Methods that measure the mass or volume under [[Denaturation (biochemistry)|unfolding]] conditions (such as 
[[Matrix-assisted laser desorption/ionization|MALDI-TOF]] [[mass spectrometry]] and [[Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis|SDS-PAGE]]) are generally not useful, since non-native conditions usually cause the complex to dissociate into monomers. However, these may sometimes be applicable; for example, the experimenter may apply SDS-PAGE after first treating the intact complex with chemical [[cross-link]] reagents.