Assay Biuret

Cyanuric acid can also be prepared by pyrolysis of urea derivatives. Biuret and triuret give less aminotria ines due to reduced ammonia evolution. Urea cyanurate also provides a higher assay product. 

For the assay of ephedrine in the total alkaloids a colorimetric method based on the biuret reaction was used by Feng and Read and is described in detail by Feng. Krishna and Chose separated ephedrine and iji-ephedrine by treating the dry mixed hydrochlorides with dry chloroform in which the ephedrine salt is virtually insoluble and the -ephedrine salt soluble. ... 

The abundance and ease of purification made bovine serum albumin (BSA) an early standard in protein chemistry, and BSA is widely used as protein standard in biuret, Lowry, and Bradford assays as well as a molecular weight... 

Review methods for protein assay including absorbance and colorimetric (Lowry, Biuret, Bradford, BCA). 

Preparation of Tubes for the Biuret Protein Assay on Mitochondrial Fractions1... 

Estimate the protein concentration using the biuret assay. If necessary, dilute to 1 mg protein/mL. 

B 9. A student group completed the biuret assay on their mitochondrial preparation. Assume that the following absorbance values were obtained as described in Table E10.2. 

Basic Protocol 3 The Biuret Assay for Determining Total Protein Bl.l. 10... 

Alternate Protocol 5 Microtiter Plate Biuret Assay for Total Protein B1.1.13... 

This unit describes four of the most commonly used total protein assay methods. Three of the four are copper-based assays to quantitate total protein the Lowry method (see Basic Protocol 1 and Alternate Protocols 1 and 2), the bicinchoninic acid assay (BCA see Basic Protocol 2 and Alternate Protocols 3 and 4), and the biuret method (see Basic Protocol 3 and Alternate Protocol 5). The fourth is the Coomassie dye binding or Bradford assay (see Basic Protocol 4 and Alternate Protocols 6 and 7), which is included as a simple and sensitive assay, although it sometimes gives a variable response depending on how well or how poorly the protein binds the dye in acidic pH. A protein assay method should be chosen based on the sensitivity and accuracy of method as well as the condition of the sample to be analyzed. 

Table B1.1.3 Troubleshooting Guide for Biuret Protein Assay...

MICROTITER PLATE BIURET ASSAY FOR TOTAL PROTEIN... 

The biuret assay can be performed in a 96-well microtiter plate and has a working concentration of 10 to 160 mg/ml. 

The biuret total protein reagent is considerably less sensitive to total protein than the other three protein assay reagents discussed in this unit. This limits the applications in which the Biuret reagent can be used. Since the primary use of the Biuret reagent has been for serum total protein in the clinical laboratory, there is little published information about its compatibility with substances and reagents common to nonclinical samples. 

Beyer, R.E. 1983. A rapid biuret assay for protein of whole fatty tissues. Anal. Biochem. 129 483-485. 

Watters, C. 1978. A one-step biuret assay for protein in the presence of detergent. Anal. Biochem. 88 695-698. 

Many methods are available for measuring TCA-soluble peptides. Possibly the easiest is to measure the absorbance of the solution at 280 nm, as the absorbance at this wavelength is a function of the aromatic amino acid content of the solution. This approach requires a UV spectrophotometer, and the sensitivity of the assay is likely to be lower than that of some of the colorimetric assays. There are also several colorimetric peptide assays that can be applied to this type of peptidase assay, such as the Biuret, Lowry, and Bradford dye-binding methods (for comparison see Piyachomkwan and Penner, 1995). All of these methods measure a relative value rather than an absolute amount of peptide in solution. The results should thus be reported in terms of equivalents, such as BSA equivalents when using a calibration curve prepared using a BSA standard solution. 

Bicinchoninic acid (BCA), total protein determination, 77-104 Bilirubin, in BCA protein assay, 96 Binding, water, see Water retention Biological value (BV), protein quality, 128-129, 133 Biuret assay... 

Bovine gamma globulin (BGG), total protein determination BCA assay, 84 (fig.) biuret assay, 88 (fig.), 98 Coomassie plus assay, 90 Bovine serum albumin (BSA), total protein determination BCA assay, 84 (fig.) biuret assay, 88 (fig.), 98 Coomassie plus assay, 90 protein standards, 78... 

In the Biuret reaction, a purple colour develops when the protein is treated with alkaline copper sulphate. This reaction is dependent on peptide bonds and not on the side chains of individual amino-acids present. In the Folin-Ciocalteu reaction, the protein is treated with tungstate and molybdate under alkaline conditions and the formation of a complex such phenylalanine and tyrosine gives rise to a blue colour. Lowry developed one of the most widely used protein assays in which a combination of the above reactions is involved07, l8). 

Protein Determinations The biuret assay (23) was employed for determining protein in tissue samples. 

The Folin-Ciocalteau Assay of Protein Concentration. The Folin-Ciocalteau assay is one of the most sensitive and most commonly used assays to determine protein concentration (sensitive to about 10 /rg/m I protein). This procedure employs two color-forming reactions to assay protein concentration photometrically. In the first reaction (a biuret reaction), compounds with two or more peptide bonds form a dark blue-purple color in the presence of alkaline copper salts. In the second reaction, tryptophan and tyrosine side chains react with the Folin solution to produce cuprous ions. This reaction is most efficient under basic condi-... 

---