USE OF EXCLUDED-VOLUME TO INCREASE THE HETEROGENEITY OF PORE-SIZE IN AGAROSE GELS

When testing theoretical models that quantitatively describe the sievi ng of macromolecules during gel electrophoresis, investigators have be en limited by absence of control of the heterogeneity of the size of p ores in the gel. In a recent study performed by electron microscopy of thin sections (G. A. Griess et al., J. Struct. Biol. 1993, 111, 39-47 ), pore size heterogeneity has been increased for agarose gels by a co mbination of both derivatization and molecular weight reduction of the polysaccharide chains of agarose. In the present study, pore size het erogeneity is increased by a mechanism that appears to have an origin different from the origin of this previously observed increase in hete rogeneity: Pore size heterogeneity is increased by addition of a polye thylene glycol (PEG) of high molecular weight (18 500) to molten agaro se before gelation. In contrast, the use of a lower molecular weight P EG (either 4 000 or 7500) causes the formation of micron-sized precipi tates within a gelled network of agarose fibers. Thus far, the PEG-ind uced heterogeneity of pore size occurs primarily in 100-1000 mu m scal e zones separated from each other by interzone regions of decreased ag arose fiber density. More uniform gels are needed for the study of sie ving.