I have run the regular SDS Page laemmeli's method.But the resolution of low molecular weight proteins is poor in coomassie.I have run in 12% gel and am looking for proteins between 6kD and 20 kD.I changed different buffers,protease inhibitors and denaturing buffers.But the samples behave the same in gel(low resolution of low mol wt proteins).Then I changed my 30% acrylamide solution.Still the problem persists.Please help me out.

Kanmani:

These references may be of some help to you...

Notice that Dean et al was able to use an SDS-PAGE method to resolve proteins in the range of 5-200kDa and 2-17kDa.


T. P. Dean, M. C. A. Clarke, J. O'B Hourihane, K. R. Dean, J. O. Warner (1996) Application of an electrophoretic methodology for the identification of low molecular weight proteins in foods . Pediatric Allergy and Immunology 7 (4), 171175.
doi:10.1111/j.1399-3038.1996.tb00128.x

Abstract:
Identification and characterisation of food proteins are core features of food allergy research. Current methods used to identify allergenic proteins in food have insufficient resolution and are unable to delect low molecular weight proteins. In this study we report the use of a simple SDS-PAGE method which allows resolution of small proteins. We have subsequently applied this method and reported presence of low molecular weight proteins in a range of hydrolysed milk formulae (Nutramigen, Pregistimil, Alfare, Pepti-Junior and Pregomin), and crude peanut protein extract. The molecular weight distribution for the peanut extract and the hydrolysates ranged between 5-200kDa and 2-17kDa respectively.




R. Singh, A. K. Shasany, A. Aggarwal, S. Sinha, B. S. Sisodia, S. P. S. Khanuja, R. Misra (2007). Low molecular weight proteins of outer membrane of Salmonella typhimurium are immunogenic in Salmonella induced reactive arthritis revealed by proteomics . Clinical & Experimental Immunology 148 (3), 486493.
doi:10.1111/j.1365-2249.2007.03362.x

Abstract:
In patients with reactive arthritis (ReA)/undifferentiated spondyloarthropathy (uSpA), synovial fluid mononuclear cells (SFMC) show proliferation to bacterial antigens that trigger ReA, i.e. Chlamydia, Yersinia, Campylobactor, Shigella and Salmonella species. We have shown previously that SFMC proliferate significantly to outer membrane proteins of S typhimurium in Salmonella induced ReA. In the present study we characterized the immunoreactive fractions of outer membrane protein (Omp) of S typhimurium in Salmonella induced ReA. Omp of Salmonella was isolated and fractionated by continuous elution sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) using Prep-Cell into eight Omp fractions based on molecular weight. Twenty-three patients with ReA were screened for the bacterial trigger using the SFMC proliferative response to crude lysates of Y enterocolitica, S flexneri, C jejuni and S typhimurium using thymidine uptake assay. SFMC from patients with salmonella induced ReA were tested against eight fractions. Seven of 23 patients with ReA had S typhimurium-induced ReA. Of these seven patients, five patients SFMC had a significant stimulation index (SI) against < 22, 2226, 2535 and 2840 kDa fractions of Omp. These fractions were analysed by SDS-PAGE and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, which revealed 10 proteins. These proteins were 37 kDa OmpA, 33 kDa TsX, 28 kDa putative Omp, 28 kDa Vac J, 39 kDa OmpD, 18 kDa OmpX, 23 kDa OmpW, 43 kDa OmpS1 and 19 kDa peptidoglycan-associated lipoprotein. In conclusion, for the first time we have identified some low molecular weight proteins in the Omps of Salmonella which are T cells immunoreactive in patients with salmonella induced ReA/uSpA.



The
Sigma Molecular Weight Markers are available in ultra-low range weight ranges. The ultra-low range marker is suitable for use in a Tricine SDS-PAGE system.

Thanks Tony,I'll try this new method

Great! Would you please post your results to the board. It would be very helpful to know if this worked for you or not.