Electrophoresis in density gradients of metrizamide

Linear density gradients of metrizamide have been used to prevent convection during electrophoresis in an apparatus originally designed for use with cylindrical gels. The procedures used are comparatively easy to perform. Two capsids of bacteriophage T7 previously shown to differ in average electrical surface charge density (σ) have been separated from each other by electrophoresis in gradients of metrizamide. These capsids were cleanly separated from both T7 DNA and a complex of a T7 capsid with T7 DNA. Thus, electrophoresis in density gradients of metrizamide is a technique for separating capsid-DNA complexes from DNA-free capsids and should be capable of separating other supramolecular complexes and organelles which differ in σ, some of which may be too large to be separated by electrophoresis in gels.