Protein molecular weight markers, sometimes referred to as protein standards or protein ladders, are used to estimate the molecular weight of proteins of interest and to monitor the progress of electrophoretic separation or transfer in Western blotting. Unstained molecular weight markers usually consist of a mixture of purified native or recombinant proteins of defined molecular weights. Visualizing their location on a gel or membrane requires a staining step. Pre-stained protein markers allow easy tracking of electrophoretic separation and transfer efficiency. Individual protein standards are also available for protein electrophoresis, isoelectric focusing, and 2D-PAGE applications.
ColorBurst Markers are composed of eight polypeptides that have been chemically reduced and conjugated to brilliantly colored dyes. Colorburst markers can be used to estimate sample molecular weights, monitor the progress of an electrophoretic run, or confirm completion of electroblotting.
SigmaMarker™ protein markers are designed for use with SDS-PAGE and cover the range of molecular weights common to most proteins or their subunits. These high and low wide range markers are lyophilized with sample buffer so that they are ready-to-use after reconstitution with deionized water. The markers are formulated to yield a distribution of well-defined bands of approximately equal intensity after electrophoresis and Coomassie blue staining.
Perfect Protein Markers were designed for routine use in SDS-PAGE to enable highly accurate size determination of unknown samples. Unlike many conventional markers (e.g., ovalbumin, serum albumin), Perfect Protein Markers contain no oligosaccharides that cause anomalous migration, heterogeneous "fuzzy" bands, or inaccurate size estimation. These markers are optimized for use with Coomassie blue staining, but adjusted amounts can also be used with other gel staining methods including silver staining and staining with fluorescent dyes.
Ultra-low Range Molecular Weight Markers (M.W. 1,060-26,600) have been used as protein markers in SDS-PAGE and Western blotting. Fixing is recommended.
Non-denaturing markers have been used as standards for native PAGE, as well as to calibrate columns for gel exclusion chromatography.
Biotinylated protein markers
The Biotinylated Molecular Weight Standard Mixture contains proteins that are biotin-conjugated for use as both SDS-PAGE standards and as standards for Western blotting. Visualization is accomplished using streptavidin-peroxidase with an appropriate colorimetric or luminescent substrate. These markers can be detected simultaneously with immunostaining procedures.