Other Sdspage Systems

The SDS-PAGE technique may also be performed with the simpler continuous phosphate buffer system of Weber and Osbourne, although dilute samples are not concentrated by stacking as they are in the discontinuous system of Laemmli. In general, however, very dilute protein samples may be concentrated by precipitation with trichloroacetic acid or acetone prior to loading.

Separations of peptides and protein mixtures ranging in molecular weight from 300 kDa down to about 10-12 kDa may be optimally achieved using resolving gels of different fixed acrylamide concentrations as, for instance, shown in Figure 3A (7.5%) or B (10%) for the separation of phosphoproteins during the invasion of human red blood cells by the malarial parasite. Alternatively, a gradient mixer may be used to produce resolving gels with a linear or concave concentration gradient.

Peptides of less than 10 kDa are not resolved using the normal Laemmli system even at maximal acryl-amide concentration so a variety of modified buffer systems have been introduced to allow the separation of, for example, cyanogen bromide and proteolyti-cally cleaved peptides for structural analysis of proteins. The original Swank and Monkres system uses SDS/urea and is capable of resolution down to 2 kDa, although some undesirable modifications of amino acids may take place in the presence of urea. Other buffer systems designed to fractionate low molecular weight peptides such as the tricine and the modified Laemmli system have been more recently introduced to address this problem. For a detailed technical discussion of the preparation of gels using these various

12 000

10 000


1 6000



<1970 1975 1980 1985 1990 1995 2000 Year

Figure 2 The number of SCI citation of the original Laemmli, U.K. (1970) paper on sodium dodecyl sulfate-polyacrylamide gel electrophoresis for each year from 1974 (when SCI started).

buffer systems one should refer to one or more of the following generally excellent technical guides available (Current Protocols in Molecular Biology; Gel Electrophoresis of Proteins - A Practical Approach; Protein Purification, Principles - High Resolution Methods and Techniques).

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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