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Mix thoroughly by vortexing and incubate for 30 minutes at 25°C. Transfer to suitable cuvettes and record the absorbance at 540 nm for Test, ...
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Biuret Method PRINCIPLE: Copper + Protein Alkaline pH> Copper-protein complexes CONDITIONS: T = 25°C, A540nm, Light path = 1 cm METHOD: Colorimetric REAGENTS: A. 0.85% (w/v) Sodium Chloride Solution (NaCl) (Use Sodium Chloride Solution, 0.85%, Sigma Stock No. 430AG-4 or prepare 100 ml in deionized water using Sodium Chloride, Sigma Prod. No. S-9625.) B. 0.5% (w/v) Working Protein Standard (WPS) (Use WPS prepared per Sigma "Preparation of Working Protein Standard for use in Protein Determination Procedure." (See attached procedure) C. Biuret Reagent (Biuret) (Use Total Protein Reagent, Sigma Stock No. 541-2.) D. Protein Sample Solution (Protein) (Prepare a solution containing 0.5 - 4 mg protein/ml of Sample in Reagent A.) PROCEDURE: Pipette (in milliliters) the following reagents into suitable containers: Test Std 1 Std 2 Std 3 Std 4 Std 5 Blank Reagent A (NaCl) ---- 0.96 0.90 0.80 0.40 ---- 1. Reagent B (WPS) ---- 0.04 0.10 0.20 0.60 1.00 ---- Reagent D (Protein) 1.00 ---- ---- ---- ---- ---- ---- Mix by swirling. Then add: Reagent C (Biuret) 4.00 4.00 4.00 4.00 4.00 4.00 4. Mix thoroughly by vortexing and incubate for 30 minutes at 25°C. Transfer to suitable cuvettes and record the absorbance at 540 nm for Test, Standards, and Blank.
Biuret Method CALCULATIONS: r A540nm Standard = A540nm Std - A540nm Std Blank Prepare a standard curve by plotting the A540nm of the Standards vs mg of protein. Sample Determination: r A540nm Sample = r A540nm Test - A540nm Test Blank Determine the mg of protein using the Standard curve. mg Protein = (mg of protein from the Standard curve)(df) (mg Protein) (100) % Protein = ___________________________ (mg solid/ml Reagent D)
For Products that are liquid: (mg Protein) mg Protein/ml = _________________ (ml Reagent D) 100 = Conversion to percentage REFERENCES: Gornall, A.G., Bardawill, C.J. and David, M.M. (1949) J. Biol. Chem. 177 , 751- Ryan, M.T. and Chopra, R.K. (1976) Biochim. Biophys. Acta 427 , 337- NOTES: