Electrophoresis of flexible macromolecules: evidence for a new mode of transport in gels.

Movement of macromolecules through low concentration agarose gels was investigated with linear poly(styrenesulfonate), linear DNA, star-shaped poly(styrenesulfonate), and circular DNA. Mobilities of weakly entangled flexible macromolecules were independent of molecular radius; within a homologous chemical sequence, electrophoretic separation at low field strengths depended solely on the degree of polymerization. These observations cannot be explained either by sieving or by reptation mechanisms; transport was apparently controlled by spatial variations of chain configurational entropy. Only when the chain was highly entangled did chain topology affect mobility. Evidence for entropically regulated transport clarifies how gel electrophoresis separates flexible macromolecules.