Proteins Biuret procedure

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-... 

Procedure 11.1 Quantitation of protein using the Biuret reaction ... 

K7. Kingsley, G. 11., Procedure for serum protein determinations with a triphosphate biuret reagent. Stand. Methods Clin. Chem. 7, 199-207 (1972). 

El88 Barnes, D.B., Pierce, G.F., Lichti, D., Landt, M., Koenig, J. and Chan, K.-M. (1985). Effects of dextran on five biuret-based procedures for total protein in serum. Clin. Chem. 31, 2018-2019. 

The determination of total serum protein is an important clinical measurement used in diagnosing liver malfunctions. Although the Kjeldahl method is capable of high precision and accuracy, it is too slow and cumbersome to be used routinely in determining total serum protein. The Kjeldahl procedure, however, has historically been the reference method against which other methods are compared. Methods commonly used include the Biuret method and the Lowry... 

Albumin and globulins can be analyzed by the same procedure as for total proteins after fractionation by salting out with either sodium sulfate or sodium sulfite. More detailed information may be required about the protein fractions (a, j8, 7 globulins), in which case starch gel electrophoresis can be used to separate the proteins. Micro-Kjeldahl analysis of proteins is used when highly accurate data are required the biuret method is accurate to about 4%. 

Lipids of plasma and liver homogenate were extracted by the procedure of Folch et al (1957). The fatty acid composition was determined using gas liquid chromatography. Blood glucose was measured by the o-toluidine method (Dubowsky, 1962) and liver glycogen by the method of Van Handel (1965). Proteins were determined by the biuret method of Gornall et al (1949) and liver cyclic AMP by the method of Mato and Serrano Rios (1973). 

The most widely used procedure for determining protein by the biuret reaction seems to be that of Kingsley (112) though several earlier publications (113,114,115,116) have appeared. Kingsley s applications were entirely to blood proteins. Campbell and Hanna (117), Sunderman and Schmidt (118) and Andersch (119) studied the application to cerebrospinal fluid, while Johnson (120) applied it to analysia of allergenic extracts. 

---