This is widely known. Well established journals seem to accept structural work if the SDS-PAGE (with Coomassie Blue stain) show >95% purity. There is another disturbing practice which is occasionally

seen that the band of the protein is shown at far end of the lane. This rules out detecting the presence of any proteolytic fragments or contaminating proteins click here of lower molecular weight. Not all applications of the proteins require the same level of purity. This is an important point since there is a three way trade-off between purity vs. number of steps vs. cost of production (Figure 1). Industrial enzymes used in many industries do not require high purity. Reasonable level of specific activity GSK2118436 molecular weight is sufficient. Proteins used for pharmaceutical applications (e.g. monoclonal antibodies or clot busters, hormones, etc.) not only require extremely high purity; regulatory agencies require that these preparations are specifically free of certain contaminants (Anicetti and Hancock, 1994 and Walsh and Headon, 1994) (Table 2). There is also a fairly widespread practice of measuring Km, Vmax and stability of proteins which are fairly impure. Unless, the preparation is standardized with respect to contaminants (like in commercially available industrial enzymes), such data actually cannot be relied upon (the reason for this is explained

later on). Finally, as may be clear from the above discussion, protein purity is a relative term. One of the most well characterized enzymes is bovine pancreatic RNase A (Richards and Wyckoff, 1971). Most of the work, including X-ray crystallography, has been carried out with a “pure” preparation obtained by Cell Penetrating Peptide a final ion-exchange chromatographic step (Richards and Wyckoff, 1971). However, this preparation shows multiple proteins when subjected to multiple counter-current distribution process (Richards and Wyckoff, 1971)! In general, crystallization can be both a purification strategy (Przybycien et al., 2004) as well as a criterion of reasonable purity (Dixon et al., 1979). Precipitation,

both with and without an interface with affinity interactions is another efficient, simple and scalable approach (Mondal et al., 2006, Mondal and Gupta, 2006 and Niederauer and Glatz, 1992). Most of the industrial enzymes these days are produced by recombinant methods wherein overexpression leads to a considerably less heterogeneous protein preparation. Many proteins upon overexpression in Escherichia coli as host end up as inclusion bodies. In recent years, in many cases these inclusion bodies are being considered as carrier-free immobilized preparation of fairly pure enzymes ( Garcia-Fruitos et al., 2012). One of the key parameters in biocatalysis is the amount of protein present in the biocatalyst preparation.