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How do we evaluate a purification protocol? Table 3.1 Quantification of a purification protocol for a fictitious protein Total protein Total activity Specific activity Yield Purification Step (mg) (units) (units mg-1) (%) level Homogenization 15,000 150,000 10 100 Salt fractionation 4,600 138,000 30 W - 92 lon-exchange chromatography 1,278 115,500 90 77 9 Gel-filtration chromatography 68.8 75,000 1,100 50 110 Affinity chromatography 1.75 52,500 30,000 35 3,000 Table 3.1 Biochemistry, Seventh Edition 2012 W. H. Freeman and Company total activity specific activity = total protein % yield = current total activity original total protein X100 purification level = current specific activity original specific activity 14