Bio-Rad Criterion™ XT Tris-Acetate Precast Gels - Manual (Page 5)

1.2 Criterion XT Precast Gels
Criterion XT precast gels are formulated at pH near neutrality to optimize gel matrix stability, significantly
delaying acrylamide hydrolysis, which occurs in traditional Laemmli systems. Specially optimized buffers
result in tight, consistently resolved bands throughout the life of the gel.
This versatile system allows the separation of small to large proteins using just two gel buffer systems:
Criterion XT Bis-Tris precast gels for small to mid-sized proteins and Criterion XT Tris-acetate precast gels for
large proteins.
The Criterion XT Bis-Tris gels are based on a Bis-Tris.HCl buffer system (pH 6.4) that uses discontinuous
chloride and MES or MOPS ion fronts to form moving boundaries to stack and then separate denatured
proteins by size. The chemistry of the XT Bis-Tris gels allows maximum stability and consistent results for a
minimum of one year. Running the same XT Bis-Tris gels with the XT MES denaturing running buffer or the XT
MOPS denaturing running buffer will produce different migration patterns. A combination of these two running
buffers and our three XT Bis-Tris gels can produce up to six different migration patterns in the small and mid-
size range.
The Criterion XT Tris-acetate gels are based on a Tris-acetate buffer system (pH 7.0). It uses discontinuous
acetate and Tricine ion fronts to form moving boundaries to stack and then separate large denatured proteins
by molecular weight. The Criterion XT Tris-acetate gels can also be used to separate proteins by their charge-
to-mass ratio (under native-PAGE conditions). This is possible because the XT Tris-acetate gels are made
without SDS, allowing the sample buffer and running buffer to dictate the separation mechanism. The
nonreducing and nondenaturing environment of native PAGE allows the detection of biological activity and
can improve antibody detection. Native PAGE can also be used to resolve multi-protein bands where
molecular mass separation by SDS-PAGE would reveal only one and for the separation of intact protein
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