appropriate blank.Interference caused by detergents,sucrose.and EDTA can be eliminated by of precipitation step(sNote 1). 7.The amount of coo produced in this assay by any given protein (or mixture of proteins)is dependent on the amino acid composition of the protein(s)(see Introduction).Therefore,two different proteins.each for example at concentrations of I mg/mL can give different color yields in this assay.It must be appreciated.therefore.that using bovine serum albumin(BSA)(or any eony time when this method gives an absolutealue for protein is when the protein being analyzed is also used to construct the standard curve.The most accurate way to determine the concentration of any protein solution is amino acid analysis. Protein Determination by UV Absorption 1.Principle Protein solutions have a great ultraviolet (UV)absorption at the wavelength of 280nm.Absorption of radiation in the near UV (A28o,or OD2so)by proteins depends on the Tyr and Trp content(and to a very small extent on the amount of Phe and disulfide bonds).So quantitation of the amount of protein in a solution n is possible a simple spectrometer The advantages of this method are that it is simple,and the sample is recoverable. The method has some disadvantages,including interference from other chromophores. and the specific absorption value for a gi ven protein must be determined.The extinctio in the 2-mregio may be as much s 10 times that protein at their same wavelength,and hence,a few percent of nucleic acid can greatly influence the absorption. 2.Materials 2.1.standard protein solution:bovine serum albumin(BSA)solution at 1 mg/ml 2.2 sample (unknown concentration,here we use I mg/ml casein). 2.3 UV-visible spectrometer:The hydrogen lamp should be selected for maximum intensity at the particular wavelength. 3.Methods 3.1 Prepare the standard curve Take 8 tubes and work as the following table: Tube No. Reagents 1 2 3 4 5 6 7 8 Standard(ml) 0 0.50 1.00 1.50 2.002.503.00 4.00 H2O (ml) .003.503.002.502.001.501.00 Concentration(mg/ml)0 0.1250.2500.3750.5000.6250.7501.000 Mix up the reaction system,and measure the A2so with 752-type spectrometer. 6